Solution.java

//Problem: https://www.hackerrank.com/challenges/cavity-map
//Java 8

//Cavity Map

//n x n matrix

// Cavity = L, R, T, B  < Cavity.value  && not on border
// Mark all cavitys with X

//matrix type is positive integers 1-9
// 1<= n <= 100

/*
input:
n
n----
| - | 
----n
    
1 

2 2
2 2

3 3 3
3 3 3
3 3 3

4 4 4 4 
4 4 4 4 
4 4 4 4
4 4 4 4 
  
*/

//iterate through inner matrix
//Check L, R, T, B  != X &&  < current value
//Add to a list




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 input = new Scanner(System.in);
        int n = input.nextInt();
        input.nextLine();
        int[] map = new int[n*n];
        
        int index = 0;
        //Initialize our n*n matrix   
        for(int i = 0; i < n; i++)
        {
            String row = input.nextLine();
            
            for(int j = 0; j < n; j++)
            {
                
                map[index++] = Character.getNumericValue(row.charAt(j));;
            }
        }
        
        for(int num : map)
        {
           // System.out.println("array "+num);
        }
        
        
        for(int i = 0; i < n*n; i++)
        {    
            //If it is not on the border
            if(i % n != 0 && (i-(n-1)) % n != 0 && i > n-1 && i < (n*n)-n)
            {
                //Left
                int L = map[i-1];    
                
                //Right
                int R = map[i+1];
                
                //Top
                int T = map[i-n];
                
                //Bottom
                int B = map[i+n];
                
                //if they are all < this is cavity print x
                if(L < map[i]  && R < map[i] && T < map[i] && B < map[i])
                {
                    System.out.print("X");
                    continue;
                }
            }
            
            System.out.print(map[i]);
            
            //If this is the right edge start a new line
            if((i-(n-1)) % n == 0)
            {
                System.out.println("");
            }
        }
    }
}