Cavity Map – HackerRank Solution

In this post, we will solve Cavity Map HackerRank Solution. This problem (Cavity Map) is a part of HackerRank Problem Solving series.

Contents

Task

You are given a square map as a matrix of integer strings. Each cell of the map has a value denoting its depth. We will call a cell of the map a cavity if and only if this cell is not on the border of the map and each cell adjacent to it has strictly smaller depth. Two cells are adjacent if they have a common side, or edge.

Find all the cavities on the map and replace their depths with the uppercase character X.

Example

grid = [‘989’, ‘191’, ‘111’]

The grid is rearranged for clarity:

989
191
111

Return:

989
1X1
111

The center cell was deeper than those on its edges: [8,1,1,1]. The deep cells in the top two corners do not share an edge with the center cell, and none of the border cells is eligible.

Function Description

Complete the cavityMap function in the editor below.

cavityMap has the following parameter(s):

  • string grid[n]: each string represents a row of the grid

Returns

  • string{n}: the modified grid

Input Format

The first line contains an integer n, the number of rows and columns in the grid.

Each of the following n lines (rows) contains n positive digits without spaces (columns) that represent the depth at grid[row, column].

Constraints

  • 1 <= n <= 100

Sample Input

STDIN   Function
-----   --------
4       grid[] size n = 4
1112    grid = ['1112', '1912', '1892', '1234']
1912
1892
1234

Sample Output

1112
1X12
18X2
1234

Explanation

The two cells with the depth of 9 are not on the border and are surrounded on all sides by shallower cells. Their values are replaced by X.

Solution – Cavity Map – HackerRank Solution

C++

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main(){
    int n;
    cin >> n;
    vector<string> grid(n);
    for(int grid_i = 0;grid_i < n;grid_i++){
       cin >> grid[grid_i];
    }
    char **answer = new char*[n];
    for(int i = 0; i < n; i++) {
        answer[i] = new char[n];
        for(int j = 0; j < n; j++) {
            answer[i][j] = grid[i][j];
        }
    }
    for(int i = 1; i < n-1; i++) {
        for(int j = 1; j < n-1; j++) {
            if(grid[i][j] > grid[i-1][j] && grid[i][j] > grid[i][j-1] && grid[i][j] > grid[i][j+1] && grid[i][j] > grid[i+1][j]) {
                answer[i][j] = 'X';
            }
        }
    }
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            cout<<answer[i][j];
        }
        cout<<"\n";
    }
    return 0;
}

Python

import sys

def cavityMap(grid):
    leng = len(grid)
    output = [[0]*leng for _ in range(leng)]
    
    for ind in range(leng):
        for jnd in range(leng):
            if (0 < ind < leng-1 and 0 < jnd < leng-1 and
               grid[ind][jnd] > grid[ind+1][jnd] and
               grid[ind][jnd] > grid[ind-1][jnd] and
               grid[ind][jnd] > grid[ind][jnd+1] and
               grid[ind][jnd] > grid[ind][jnd-1]):
                output[ind][jnd] = 'X'
            else:
                output[ind][jnd] = grid[ind][jnd]
    
    return output

if __name__ == "__main__":
    n = int(input().strip())
    grid = []
    grid_i = 0
    for grid_i in range(n):
        grid_t = list(map(int, input().strip()))
        grid.append(grid_t)
    result = cavityMap(grid)
    print("\n".join(["".join(map(str, x)) for x in result]))

Java

import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner in = new Scanner(System.in);
        int n = Integer.parseInt(in.nextLine());
        int[][] array = new int[n][n];
        int[][] target = new int[n][n];
        for(int i=0; i<n; i++){
            String line = in.nextLine();
            char[] data = line.toCharArray();
            for(int j=0; j<n; j++){
                array[i][j] = Character.getNumericValue(data[j]);
                //System.out.println(array[i][j]);
            }
        }
        cavityMap(array, target);
        for(int i=0; i<n; i++){
            for(int j=0; j<n; j++){
                if(target[i][j] == -1)
                    System.out.print("X");
                else
                    System.out.print(array[i][j]);
            }
            System.out.println("");
        }
    }
    
    public static void cavityMap(int[][] array, int[][] target) {
        int row = array.length;
        int col = array[0].length;
        for(int i=1; i<row-1; i++){
            for(int j=1; j<col-1; j++){
                if(isMaximum(array, i, j)){
                    target[i][j] = -1; // will be translate to X later
                }
            }
        }
    }
    
    public static boolean isMaximum(int[][] array, int i, int j) {
        int max = Math.max(Math.max(array[i-1][j], array[i+1][j]), Math.max(array[i][j-1], array[i][j+1]));
        if(max >= array[i][j])
            return false;
        else
            return true;
    }
}

Note: This problem (Cavity Map) is generated by HackerRank but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.

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