In this post, we will solve Build a Palindrome HackerRank Solution. This problem (Build a Palindrome) is a part of HackerRank Problem Solving series.
Solution – Build a Palindrome – HackerRank Solution
C++
#include <bits/stdc++.h> using namespace std; #ifndef SUFFIXARRAY_H_INCLUDED #define SUFFIXARRAY_H_INCLUDED #include <algorithm> #include <vector> class suffix_array { public: std::vector<int> suftab[2]; std::vector<int> order; std::vector<int> sufarr; std::vector<int> bucket_count, bucket_size; std::vector<int> lcp; // lcp(sa[i], sa[i+1]) == sa.lcp[i] template<class T> void build_sa(T S[], int N) { suftab[0].resize(N); suftab[1].resize(N); order.resize(N); sufarr.resize(N); bucket_count.resize(N+1); bucket_size.resize(N+1); for(int i=0; i<N; i++) order[i]=S[i]; std::sort(order.begin(), order.end()); for(int i=0; i<N; i++) suftab[0][i]=std::lower_bound(order.begin(), order.end(), S[i])-order.begin(); int lg=0; while((1<<lg)<N) lg++; int row=0; for(int hlen=1; hlen<(1<<lg); hlen*=2, row^=1) { bucket_count.assign(N+1, 0); int pos=0; for(int i=0; i+hlen<N; i++) bucket_count[suftab[row][i+hlen]+1]++; for(int i=N-hlen; i<N; i++) order[pos++]=i; bucket_count[0]=pos; std::partial_sum(bucket_count.begin(), bucket_count.end(), bucket_size.begin()); for(int i=0; i+hlen<N; i++) order[bucket_size[suftab[row][i+hlen]]++]=i; bucket_count[0]=0; for(int i=0; i<hlen; i++) bucket_count[suftab[row][i]+1]++; std::partial_sum(bucket_count.begin(), bucket_count.end(), bucket_size.begin()); for(int i=0; i<N; i++) sufarr[bucket_size[suftab[row][order[i]]]++]=order[i]; int prev_a=-1, prev_b=-1, prev_c=-1; for(int i=0; i<N; i++) { const int x=sufarr[i]; const int now_a=suftab[row][x]; const int now_b=(x+hlen<N?suftab[row][x+hlen]:-1); prev_c+=now_a!=prev_a || now_b!=prev_b; suftab[row^1][x]=prev_c; prev_a=now_a; prev_b=now_b; } } if(row==1) suftab[0].swap(suftab[1]); } template<class T> void build(T S[], int N) { build_sa(S, N); lcp.resize(sufarr.size()); for(int i=0, len=0; i<N; i++) { if(get_rank(i)==N-1) len=0; else { int j=sufarr[get_rank(i)+1]; int maxl=N-std::max(i, j); while(len<maxl && S[i+len]==S[j+len]) len++; lcp[get_rank(i)]=len; if(len>0) len--; } } } inline int get_rank(const int& idx) const { return suftab[0][idx]; } int operator[] (const int& idx) const { return sufarr[idx]; } }; #endif // SUFFIXARRAY_H_INCLUDED const int HASH_MAXN=400001; const int X=129; const int MOD1=1000000009; const int MOD2=1000000021; int P1[HASH_MAXN]; int P2[HASH_MAXN]; struct Hash { int len, val0, val1; Hash(): len(0), val0(0), val1(0) { // } Hash(int val): len(1), val0(val), val1(val) { // } Hash operator+ (const Hash& other) const { Hash ret; ret.len=len+other.len; ret.val0=(other.val0+1LL*P1[other.len]*val0)%MOD1; ret.val1=(other.val1+1LL*P2[other.len]*val1)%MOD2; return ret; } Hash operator- (const Hash& other) const { Hash ret; ret.len=len-other.len; ret.val0=val0-1LL*P1[len-other.len]*other.val0%MOD1; if(ret.val0<0) ret.val0+=MOD1; ret.val1=val1-1LL*P2[len-other.len]*other.val1%MOD2; if(ret.val1<0) ret.val1+=MOD2; return ret; } bool operator< (const Hash& other) const { if(len!=other.len) return len<other.len; if(val0!=other.val0) return val0<other.val0; return val1<other.val1; } bool operator== (const Hash& other) const { return len==other.len && val0==other.val0 && val1==other.val1; } bool operator!= (const Hash& other) const { return !(*this==other); } }; void init_hash() { P1[0]=1; for(int i=1; i<HASH_MAXN; i++) P1[i]=1LL*P1[i-1]*X%MOD1; P2[0]=1; for(int i=1; i<HASH_MAXN; i++) P2[i]=1LL*P2[i-1]*X%MOD2; } static int _hash_initialized=(init_hash(), 0); int tlen; int msuf[200001]; Hash H[200001]; Hash R[200001]; Hash get_substr(int l, int r) { if(l==0) return H[r]; return H[r]-H[l-1]; } Hash get_r_substr(int l, int r) { if(r==tlen-1) return R[l]; return R[l]-R[r+1]; } Hash get_hash(vector<pair<int, int>>& a, int l) { Hash h; for(auto& it: a) { if(l==0) break; if(abs(it.first-it.second)+1<=l) { l-=abs(it.first-it.second)+1; if(it.first>it.second) h=h+get_r_substr(it.second, it.first); else h=h+get_substr(it.first, it.second); } else { if(it.first>it.second) h=h+get_r_substr(it.first-l+1, it.first); else h=h+get_substr(it.first, it.first+l-1); break; } } return h; } char get_char(string& t, vector<pair<int, int>>& a, int l) { for(auto& it: a) { if(abs(it.first-it.second)+1<=l) l-=abs(it.first-it.second)+1; else { if(it.first>it.second) return t[it.first-l]; return t[it.first+l]; } } return '?'; } vector<pair<int, int>> get_min(string& t, vector<pair<int, int>> a, vector<pair<int, int>> b) { int la=0, lb=0; for(auto& it: a) la+=abs(it.first-it.second)+1; for(auto& it: b) lb+=abs(it.first-it.second)+1; assert(la==lb); int lo=0, mid, hi=min(la, lb); while(lo<hi) { mid=(lo+hi+1)/2; if(get_hash(a, mid)==get_hash(b, mid)) lo=mid; else hi=mid-1; } if(lo==min(la, lb) || get_char(t, a, lo)<get_char(t, b, lo)) return a; return b; } pair<int, string> solve(string s, string t) { tlen=t.length(); reverse(s.begin(), s.end()); string S=t+'#'+s; suffix_array sa; sa.build(S.c_str(), S.length()); for(int i=0; i<=(int)t.length(); i++) msuf[i]=0; int len=0; for(int i=0; i<(int)S.length(); i++) { int suf=sa[i]; if(suf<(int)t.length()) msuf[suf]=max(msuf[suf], len); else if(suf>(int)t.length() && i+1<(int)S.length()) len=max(len, sa.lcp[i]); if(i+1<(int)S.length()) len=min(len, sa.lcp[i]); } len=0; for(int i=(int)S.length()-1; i>=0; i--) { int suf=sa[i]; if(suf<(int)t.length()) msuf[suf]=max(msuf[suf], len); else if(suf>(int)t.length() && i-1>=0) len=max(len, sa.lcp[i-1]); if(i-1>=0) len=min(len, sa.lcp[i-1]); } Hash h; for(int i=0; i<(int)t.length(); i++) { h=h+Hash(t[i]); H[i]=h; } h=Hash(); for(int i=(int)t.length()-1; i>=0; i--) { h=h+Hash(t[i]); R[i]=h; } vector<pair<int, int>> ans2; int ans=0; for(int i=0; i<(int)t.length(); i++) if(msuf[i]) { if(msuf[i]*2>ans) { ans=msuf[i]*2; ans2={{i, i+msuf[i]-1}, {i+msuf[i]-1, i}}; } else if(msuf[i]*2==ans) ans2=get_min(t, ans2, {{i, i+msuf[i]-1}, {i+msuf[i]-1, i}}); } // one center for(int i=0; i<(int)t.length(); i++) { int l=min(i+1, (int)t.length()-i); int lo=1, mid, hi=l; while(lo<hi) { mid=(lo+hi+1)/2; if(get_r_substr(i-mid+1, i)==get_substr(i, i+mid-1)) lo=mid; else hi=mid-1; } if(msuf[i+lo]) { int v=2*lo-1+2*msuf[i+lo]; if(v>ans) { ans=v; ans2={{i+lo+msuf[i+lo]-1, i+lo}, {i-lo+1, i+lo+msuf[i+lo]-1}}; } else if(v==ans) ans2=get_min(t, ans2, {{i+lo+msuf[i+lo]-1, i+lo}, {i-lo+1, i+lo+msuf[i+lo]-1}}); } } // two centers for(int i=0; i<(int)t.length()-1; i++) { int l=min(i+1, (int)t.length()-(i+1)); int lo=0, mid, hi=l; while(lo<hi) { mid=(lo+hi+1)/2; if(get_r_substr(i-mid+1, i)==get_substr(i+1, i+1+mid-1)) lo=mid; else hi=mid-1; } if(msuf[i+1+lo]) { int v=2*lo+2*msuf[i+1+lo]; if(v>ans) { ans=v; ans2={{i+1+lo+msuf[i+1+lo]-1, i+1+lo}, {i-lo+1, i+1+lo+msuf[i+1+lo]-1}}; } else if(v==ans) ans2=get_min(t, ans2, {{i+1+lo+msuf[i+1+lo]-1, i+1+lo}, {i-lo+1, i+1+lo+msuf[i+1+lo]-1}}); } } string res=""; for(auto& it: ans2) { if(it.first>it.second) { for(int i=it.first; i>=it.second; i--) res+=t[i]; } else { for(int i=it.first; i<=it.second; i++) res+=t[i]; } } return make_pair(ans, res); } string _main() { string a, b; cin>>a>>b; if(a.length()<=50 && b.length()<=50) { string ans=""; for(int la=1; la<=(int)a.length(); la++) { for(int i=0; i+la-1<(int)a.length(); i++) { for(int lb=1; lb<=(int)b.length(); lb++) { for(int j=0; j+lb-1<(int)b.length(); j++) { string s=a.substr(i, la)+b.substr(j, lb); string t=s; reverse(t.begin(), t.end()); if(s==t) { if(s.length()>ans.length()) ans=s; else if(s.length()==ans.length()) ans=min(ans, s); } } } } } if(ans.empty()) return "-1"; return ans; } auto x=solve(a, b); reverse(a.begin(), a.end()); reverse(b.begin(), b.end()); auto y=solve(b, a); reverse(y.second.begin(), y.second.end()); if(max(x.first, y.first)==0) return "-1"; if(x.first>y.first) return x.second; else if(x.first<y.first) return y.second; return min(x.second, y.second); } int main() { int Q; scanf("%d", &Q); while(Q--) cout<<_main()<<endl; return 0; }
Python
def build_palindrome_lookup(s): sx = '|' + '|'.join(s) + '|' sxlen = len(sx) rslt = [0] * sxlen c, r, m, n = 0, 0, 0, 0 for i in range(1, sxlen): if i > r: rslt[i] = 0 m = i - 1 n = i + 1 else: i2 = c * 2 - i if rslt[i2] < r - i: rslt[i] = rslt[i2] m = -1 else: rslt[i] = r - i n = r + 1 m = i * 2 - n while m >= 0 and n < sxlen and sx[m] == sx[n]: rslt[i] += 1 m -= 1 n += 1 if i + rslt[i] > r: r = i + rslt[i] c = i res = [0] * len(s) for i in range(1, sxlen - 1): idx = (i - rslt[i]) // 2 res[idx] = max(res[idx], rslt[i]) return res class state: def __init__(self): self.link = -1 self.length = 0 self.childs = {} def build_part_st(a, st, num, last, sz): for c in a: cur = sz sz += 1 st[cur].length = st[last].length + 1 p = last while p != -1 and c not in st[p].childs: st[p].childs[c] = cur p = st[p].link if p == -1: st[cur].link = 0 else: q = st[p].childs[c] if st[p].length + 1 == st[q].length: st[cur].link = q else: clone = sz sz += 1 st[clone].length = st[p].length + 1 st[clone].childs = dict((x, y) for (x, y) in st[q].childs.items()) st[clone].link = st[q].link while p != -1 and st[p].childs[c] == q: st[p].childs[c] = clone p = st[p].link st[q].link = clone st[cur].link = clone last = cur return last, sz def print_st(st): i = 0 for s in st: print('#{} link:{} childs:{}'.format(i, s.link, s.childs)) i += 1 def solve(a, b): n = len(a) blen = len(b) st = [state() for x in range(2 * n)] st[0].link = -1 st[0].length = 0 last = 0 sz = 1 last, sz = build_part_st(a, st, 1, last, sz) plookup = build_palindrome_lookup(b) apos, start, left, mid, total, curlen = 0, -1, 0, 0, 0, 0 for i in range(blen): c = b[i] if c not in st[apos].childs: while apos!=-1 and c not in st[apos].childs: apos = st[apos].link if apos == -1: apos = 0 curlen=0 continue curlen = st[apos].length curlen += 1 apos = st[apos].childs[c] new_start = i - curlen + 1 new_mid = 0 if i + 1 < blen: new_mid = plookup[i + 1] new_total = 2 * curlen + new_mid if total < new_total or (total == new_total and lex_gt(b,start, new_start,curlen + mid)): left = curlen mid = new_mid total = new_total start = new_start palindrome = [] for i in range(left + mid): palindrome.append(b[start + i]) for i in range(left - 1, -1, -1): palindrome.append(palindrome[i]) return ''.join(palindrome) def lex_gt(s, old_start, new_start, size): for i in range(size): if s[old_start + i] != s[new_start + i]: if s[old_start + i] > s[new_start + i]:# old lex greater so pick new one return True break return False def suffix_automata(a,b): rb = b[::-1] # reverse b rslt1 = solve(a, rb) rslt2 = solve(rb, a) rslt = None if len(rslt1) > len(rslt2): rslt = rslt1 elif len(rslt1) < len(rslt2): rslt = rslt2 else: rslt= rslt1 if rslt1 < rslt2 else rslt2 if len(rslt) == 0: return '-1' return rslt def process_helper(a,b): return suffix_automata(a,b) for _ in range(int(input())): a = input() b = input() print(process_helper(a,b))
Java
import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.Comparator; import java.util.InputMismatchException; public class F3 { InputStream is; PrintWriter out; String INPUT = ""; void solve() { for(int T = ni();T > 0;T--){ char[] s = ns().toCharArray(); char[] t = ns().toCharArray(); String b1 = go(s, t); // tr(best); char[] rs = rev(s); char[] rt = rev(t); String b2 = go(rt, rs); if(b1 == null && b2 == null){ out.println(-1); }else if(b1 == null){ out.println(b2); }else if(b2 == null){ out.println(b1); }else if(b1.length() > b2.length() || b1.length() == b2.length() && b1.compareTo(b2) < 0){ out.println(b1); }else{ out.println(b2); } } } public static char[] rev(char[] a) { for(int i = 0, j = a.length-1;i < j;i++,j--){ char c = a[i]; a[i] = a[j]; a[j] = c; } return a; } String go(char[] s, char[] t) { char[] st = new char[s.length+t.length]; for(int i = 0;i < s.length;i++)st[i] = s[s.length-1-i]; for(int i = 0;i < t.length;i++)st[i+s.length] = t[i]; // String S = new String(s); // String ST = new String(st); int[] sa = sa(st); int nn = s.length+t.length; int[] isa = new int[nn]; for(int i = 0;i < nn;i++)isa[sa[i]] = i; int[] lcp = buildLCP(st, sa); // tr(st); // tr(sa); int[] llcp = new int[nn]; { int cur = 0; for(int i = 0;i < nn;i++){ if(sa[i] < s.length){ llcp[s.length-1-sa[i]] = cur; }else{ cur = 9999999; } if(i+1 < nn)cur = Math.min(cur, lcp[i+1]); } } int[] rlcp = new int[nn]; { int cur = 0; for(int i = nn-1;i >= 0;i--){ if(sa[i] < s.length){ rlcp[s.length-1-sa[i]] = cur; }else{ cur = 9999999; } cur = Math.min(cur, lcp[i]); } } // tr(llcp, rlcp); int[] rad = palindrome(s); // tr("s", new String(s)); // tr(rad); int[] pals = new int[s.length]; { int[][] es = new int[s.length*2-1][]; for(int i = 0;i < s.length*2-1;i++){ es[i] = new int[]{(i-rad[i]+1)/2, rad[i]}; } Arrays.sort(es, new Comparator<int[]>() { public int compare(int[] a, int[] b) { return a[0] - b[0]; } }); int p = 0; int cur = 0; for(int i = 0;i < s.length;i++){ while(p < es.length && es[p][0] <= i){ cur = Math.max(cur, es[p][1]); p++; } pals[i] = Math.max(pals[i], cur); cur = Math.max(cur-2, 0); } } // tr("pals", pals); char[] srs = new char[s.length*2]; for(int i = 0;i < s.length;i++){ srs[i] = srs[s.length*2-1-i] = s[i]; } int[] ssa = sa(srs); int[] issa = new int[srs.length]; for(int i = 0;i < srs.length;i++)issa[ssa[i]] = i; int[] slcp = buildLCP(srs, ssa); SegmentTreeRMQ sts = new SegmentTreeRMQ(slcp); int maxlen = 0; int[] lbest = null; for(int start = 0;start < s.length;start++){ int xlcp = Math.min(start+1, Math.max(llcp[start], rlcp[start])); if(xlcp == 0)continue; int lpal = start+1 < s.length ? pals[start+1] : 0; // tr(start, xlcp, lpal); int len = lpal+xlcp*2; if(len > maxlen){ maxlen = len; lbest = new int[]{start-xlcp+1, start+lpal+1, s.length-1-start+s.length, s.length-1-(start-xlcp+1)+1+s.length}; }else if(len == maxlen){ int[] can = new int[]{start-xlcp+1, start+lpal+1, s.length-1-start+s.length, s.length-1-(start-xlcp+1)+1+s.length}; int ulcp = sts.minx(Math.min(issa[can[0]], issa[lbest[0]])+1, Math.max(issa[can[0]], issa[lbest[0]])+1); if(ulcp < can[1]-can[0] && ulcp < lbest[1]-lbest[0]){ if(issa[can[0]] < issa[lbest[0]]){ lbest = can; } continue; } int L = can[1]-can[0]; int R = lbest[1]-lbest[0]; if(L < R){ int lpos = can[2], rpos = lbest[0]+L; ulcp = sts.minx(Math.min(issa[lpos], issa[rpos])+1, Math.max(issa[lpos], issa[rpos])+1); if(ulcp < R-L){ if(issa[lpos] < issa[rpos]){ lbest = can; } continue; } lpos = can[2] + R-L; rpos = lbest[2]; ulcp = sts.minx(Math.min(issa[lpos], issa[rpos])+1, Math.max(issa[lpos], issa[rpos])+1); if(issa[lpos] < issa[rpos]){ lbest = can; } }else{ int lpos = can[0]+R, rpos = lbest[2]; ulcp = sts.minx(Math.min(issa[lpos], issa[rpos])+1, Math.max(issa[lpos], issa[rpos])+1); if(ulcp < L-R){ if(issa[lpos] < issa[rpos]){ lbest = can; } continue; } lpos = can[2]; rpos = lbest[2]+L-R; ulcp = sts.minx(Math.min(issa[lpos], issa[rpos])+1, Math.max(issa[lpos], issa[rpos])+1); if(issa[lpos] < issa[rpos]){ lbest = can; } } } } if(lbest == null){ return null; }else{ StringBuilder sb = new StringBuilder(); for(int i = lbest[0];i < lbest[1];i++)sb.append(srs[i]); for(int i = lbest[2];i < lbest[3];i++)sb.append(srs[i]); return sb.toString(); } } public static class SegmentTreeRMQ { public int M, H, N; public int[] st; public SegmentTreeRMQ(int n) { N = n; M = Integer.highestOneBit(Math.max(N-1, 1))<<2; H = M>>>1; st = new int[M]; Arrays.fill(st, 0, M, Integer.MAX_VALUE); } public SegmentTreeRMQ(int[] a) { N = a.length; M = Integer.highestOneBit(Math.max(N-1, 1))<<2; H = M>>>1; st = new int[M]; for(int i = 0;i < N;i++){ st[H+i] = a[i]; } Arrays.fill(st, H+N, M, Integer.MAX_VALUE); for(int i = H-1;i >= 1;i--)propagate(i); } public void update(int pos, int x) { st[H+pos] = x; for(int i = (H+pos)>>>1;i >= 1;i >>>= 1)propagate(i); } private void propagate(int i) { st[i] = Math.min(st[2*i], st[2*i+1]); } public int minx(int l, int r){ if(l >= r)return 0; int min = Integer.MAX_VALUE; while(l != 0){ int f = l&-l; if(l+f > r)break; int v = st[(H+l)/f]; if(v < min)min = v; l += f; } while(l < r){ int f = r&-r; int v = st[(H+r)/f-1]; if(v < min)min = v; r -= f; } return min; } public int min(int l, int r){ return l >= r ? 0 : min(l, r, 0, H, 1);} private int min(int l, int r, int cl, int cr, int cur) { if(l <= cl && cr <= r){ return st[cur]; }else{ int mid = cl+cr>>>1; int ret = Integer.MAX_VALUE; if(cl < r && l < mid){ ret = Math.min(ret, min(l, r, cl, mid, 2*cur)); } if(mid < r && l < cr){ ret = Math.min(ret, min(l, r, mid, cr, 2*cur+1)); } return ret; } } public int firstle(int l, int v) { int cur = H+l; while(true){ if(st[cur] <= v){ if(cur < H){ cur = 2*cur; }else{ return cur-H; } }else{ cur++; if((cur&cur-1) == 0)return -1; if((cur&1)==0)cur>>>=1; } } } public int lastle(int l, int v) { int cur = H+l; while(true){ if(st[cur] <= v){ if(cur < H){ cur = 2*cur+1; }else{ return cur-H; } }else{ if((cur&cur-1) == 0)return -1; cur--; if((cur&1)==1)cur>>>=1; } } } } public static int[] palindrome(char[] str) { int n = str.length; int[] r = new int[2*n]; int k = 0; for(int i = 0, j = 0;i < 2*n;i += k, j = Math.max(j-k, 0)){ // normally while(i-j >= 0 && i+j+1 < 2*n && str[(i-j)/2] == str[(i+j+1)/2])j++; r[i] = j; // skip based on the theorem for(k = 1;i-k >= 0 && r[i]-k >= 0 && r[i-k] != r[i]-k;k++){ r[i+k] = Math.min(r[i-k], r[i]-k); } } return r; } private static interface BaseArray { public int get(int i); public void set(int i, int val); public int update(int i, int val); } private static class CharArray implements BaseArray { private char[] m_A = null; private int m_pos = 0; CharArray(char[] A, int pos) { m_A = A; m_pos = pos; } public int get(int i) { return m_A[m_pos + i] & 0xffff; } public void set(int i, int val) { m_A[m_pos + i] = (char) (val & 0xffff); } public int update(int i, int val) { return m_A[m_pos + i] += val & 0xffff; } } private static class IntArray implements BaseArray { private int[] m_A = null; private int m_pos = 0; IntArray(int[] A, int pos) { m_A = A; m_pos = pos; } public int get(int i) { return m_A[m_pos + i]; } public void set(int i, int val) { m_A[m_pos + i] = val; } public int update(int i, int val) { return m_A[m_pos + i] += val; } } /* find the start or end of each bucket */ private static void getCounts(BaseArray T, BaseArray C, int n, int k) { int i; for(i = 0;i < k;++i){ C.set(i, 0); } for(i = 0;i < n;++i){ C.update(T.get(i), 1); } } private static void getBuckets(BaseArray C, BaseArray B, int k, boolean end) { int i, sum = 0; if(end != false){ for(i = 0;i < k;++i){ sum += C.get(i); B.set(i, sum); } }else{ for(i = 0;i < k;++i){ sum += C.get(i); B.set(i, sum - C.get(i)); } } } /* sort all type LMS suffixes */ private static void LMSsort(BaseArray T, int[] SA, BaseArray C, BaseArray B, int n, int k) { int b, i, j; int c0, c1; /* compute SAl */ if(C == B){ getCounts(T, C, n, k); } getBuckets(C, B, k, false); /* find starts of buckets */ j = n - 1; b = B.get(c1 = T.get(j)); --j; SA[b++] = (T.get(j) < c1) ? ~j : j; for(i = 0;i < n;++i){ if(0 < (j = SA[i])){ if((c0 = T.get(j)) != c1){ B.set(c1, b); b = B.get(c1 = c0); } --j; SA[b++] = (T.get(j) < c1) ? ~j : j; SA[i] = 0; }else if(j < 0){ SA[i] = ~j; } } /* compute SAs */ if(C == B){ getCounts(T, C, n, k); } getBuckets(C, B, k, true); /* find ends of buckets */ for(i = n - 1, b = B.get(c1 = 0);0 <= i;--i){ if(0 < (j = SA[i])){ if((c0 = T.get(j)) != c1){ B.set(c1, b); b = B.get(c1 = c0); } --j; SA[--b] = (T.get(j) > c1) ? ~(j + 1) : j; SA[i] = 0; } } } private static int LMSpostproc(BaseArray T, int[] SA, int n, int m) { int i, j, p, q, plen, qlen, name; int c0, c1; boolean diff; /* * compact all the sorted substrings into the first m items of SA 2*m * must be not larger than n (proveable) */ for(i = 0;(p = SA[i]) < 0;++i){ SA[i] = ~p; } if(i < m){ for(j = i, ++i;;++i){ if((p = SA[i]) < 0){ SA[j++] = ~p; SA[i] = 0; if(j == m){ break; } } } } /* store the length of all substrings */ i = n - 1; j = n - 1; c0 = T.get(n - 1); do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) >= c1)); for(;0 <= i;){ do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) <= c1)); if(0 <= i){ SA[m + ((i + 1) >> 1)] = j - i; j = i + 1; do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) >= c1)); } } /* find the lexicographic names of all substrings */ for(i = 0, name = 0, q = n, qlen = 0;i < m;++i){ p = SA[i]; plen = SA[m + (p >> 1)]; diff = true; if((plen == qlen) && ((q + plen) < n)){ for(j = 0;(j < plen) && (T.get(p + j) == T.get(q + j));++j){ } if(j == plen){ diff = false; } } if(diff != false){ ++name; q = p; qlen = plen; } SA[m + (p >> 1)] = name; } return name; } /* compute SA and BWT */ private static void induceSA(BaseArray T, int[] SA, BaseArray C, BaseArray B, int n, int k) { int b, i, j; int c0, c1; /* compute SAl */ if(C == B){ getCounts(T, C, n, k); } getBuckets(C, B, k, false); /* find starts of buckets */ j = n - 1; b = B.get(c1 = T.get(j)); SA[b++] = ((0 < j) && (T.get(j - 1) < c1)) ? ~j : j; for(i = 0;i < n;++i){ j = SA[i]; SA[i] = ~j; if(0 < j){ if((c0 = T.get(--j)) != c1){ B.set(c1, b); b = B.get(c1 = c0); } SA[b++] = ((0 < j) && (T.get(j - 1) < c1)) ? ~j : j; } } /* compute SAs */ if(C == B){ getCounts(T, C, n, k); } getBuckets(C, B, k, true); /* find ends of buckets */ for(i = n - 1, b = B.get(c1 = 0);0 <= i;--i){ if(0 < (j = SA[i])){ if((c0 = T.get(--j)) != c1){ B.set(c1, b); b = B.get(c1 = c0); } SA[--b] = ((j == 0) || (T.get(j - 1) > c1)) ? ~j : j; }else{ SA[i] = ~j; } } } /* * find the suffix array SA of T[0..n-1] in {0..k-1}^n use a working space * (excluding T and SA) of at most 2n+O(1) for a constant alphabet */ private static void SA_IS(BaseArray T, int[] SA, int fs, int n, int k) { BaseArray C, B, RA; int i, j, b, m, p, q, name, newfs; int c0, c1; int flags = 0; if(k <= 256){ C = new IntArray(new int[k], 0); if(k <= fs){ B = new IntArray(SA, n + fs - k); flags = 1; }else{ B = new IntArray(new int[k], 0); flags = 3; } }else if(k <= fs){ C = new IntArray(SA, n + fs - k); if(k <= (fs - k)){ B = new IntArray(SA, n + fs - k * 2); flags = 0; }else if(k <= 1024){ B = new IntArray(new int[k], 0); flags = 2; }else{ B = C; flags = 8; } }else{ C = B = new IntArray(new int[k], 0); flags = 4 | 8; } /* * stage 1: reduce the problem by at least 1/2 sort all the * LMS-substrings */ getCounts(T, C, n, k); getBuckets(C, B, k, true); /* find ends of buckets */ for(i = 0;i < n;++i){ SA[i] = 0; } b = -1; i = n - 1; j = n; m = 0; c0 = T.get(n - 1); do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) >= c1)); for(;0 <= i;){ do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) <= c1)); if(0 <= i){ if(0 <= b){ SA[b] = j; } b = B.update(c1, -1); j = i; ++m; do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) >= c1)); } } if(1 < m){ LMSsort(T, SA, C, B, n, k); name = LMSpostproc(T, SA, n, m); }else if(m == 1){ SA[b] = j + 1; name = 1; }else{ name = 0; } /* * stage 2: solve the reduced problem recurse if names are not yet * unique */ if(name < m){ if((flags & 4) != 0){ C = null; B = null; } if((flags & 2) != 0){ B = null; } newfs = (n + fs) - (m * 2); if((flags & (1 | 4 | 8)) == 0){ if((k + name) <= newfs){ newfs -= k; }else{ flags |= 8; } } for(i = m + (n >> 1) - 1, j = m * 2 + newfs - 1;m <= i;--i){ if(SA[i] != 0){ SA[j--] = SA[i] - 1; } } RA = new IntArray(SA, m + newfs); SA_IS(RA, SA, newfs, m, name); RA = null; i = n - 1; j = m * 2 - 1; c0 = T.get(n - 1); do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) >= c1)); for(;0 <= i;){ do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) <= c1)); if(0 <= i){ SA[j--] = i + 1; do{ c1 = c0; }while ((0 <= --i) && ((c0 = T.get(i)) >= c1)); } } for(i = 0;i < m;++i){ SA[i] = SA[m + SA[i]]; } if((flags & 4) != 0){ C = B = new IntArray(new int[k], 0); } if((flags & 2) != 0){ B = new IntArray(new int[k], 0); } } /* stage 3: induce the result for the original problem */ if((flags & 8) != 0){ getCounts(T, C, n, k); } /* put all left-most S characters into their buckets */ if(1 < m){ getBuckets(C, B, k, true); /* find ends of buckets */ i = m - 1; j = n; p = SA[m - 1]; c1 = T.get(p); do{ q = B.get(c0 = c1); while (q < j){ SA[--j] = 0; } do{ SA[--j] = p; if(--i < 0){ break; } p = SA[i]; }while ((c1 = T.get(p)) == c0); }while (0 <= i); while (0 < j){ SA[--j] = 0; } } induceSA(T, SA, C, B, n, k); C = null; B = null; } /* char */ public static void suffixsort(char[] T, int[] SA, int n) { if((T == null) || (SA == null) || (T.length < n) || (SA.length < n)){ return; } if(n <= 1){ if(n == 1){ SA[0] = 0; } return; } SA_IS(new CharArray(T, 0), SA, 0, n, 128); } public static int[] sa(char[] T) { int n = T.length; int[] sa = new int[n]; suffixsort(T, sa, n); return sa; } public static int[] buildLCP(char[] str, int[] sa) { int n = str.length; int h = 0; int[] lcp = new int[n]; int[] isa = new int[n]; for(int i = 0;i < n;i++)isa[sa[i]] = i; for(int i = 0;i < n;i++){ if(isa[i] > 0){ for(int j = sa[isa[i]-1]; j+h<n && i+h<n && str[j+h] == str[i+h]; h++); lcp[isa[i]] = h; }else{ lcp[isa[i]] = 0; } if(h > 0)h--; } return lcp; } void run() throws Exception { is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); long s = System.currentTimeMillis(); solve(); out.flush(); if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); } public static void main(String[] args) throws Exception { new F3().run(); } private byte[] inbuf = new byte[1024]; private int lenbuf = 0, ptrbuf = 0; private int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private double nd() { return Double.parseDouble(ns()); } private char nc() { return (char)skip(); } private String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private int ni() { int num = 0, b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); } }
Note: This problem (Build a Palindrome) is generated by HackerRank but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.