Row-wise common elements in two diagonals of a square matrix

Given a square matrix, find out count of numbers that are same in same row and same in both primary and secondary diagonals.

Examples : 

Input : 1 2 1
        4 5 2
        0 5 1
Output : 2
Primary diagonal is 1 5 1
Secondary diagonal is 1 5 0
Two elements (1 and 5) match 
in two diagonals and same.

Input : 1 0 0
        0 1 0
        0 0 1
Output : 1
Primary diagonal is 1 1 1
Secondary diagonal is 0 1 0
Only one element is same.

We can achieve this in O(n) time, O(1) space and only one traversal. We can find current element in i-th row of primary diagonal as mat[i][i] and i-th element of secondary diagonal as mat[i][n-i-1].

C++



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// CPP program to find common elements in
// two diagonals.
#include <iostream>
#define MAX 100
using namespace std;
  
// Returns count of row wise same
// elements in two diagonals of
// mat[n][n]
int countCommon(int mat[][MAX], int n)
{
    int res = 0;
    for (int i=0;i<n;i++)
        if (mat[i][i] == mat[i][n-i-1])
             res++;
    return res;
}
  
// Driver Code
int main()
{
    int mat[][MAX] = {{1, 2, 3}, 
                      {4, 5, 6},
                      {7, 8, 9}};
    cout << countCommon(mat, 3);
    return 0;
}

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Java














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// Java program to find common  


// elements in two diagonals. 


import java.io.*; 


  


class GFG 


{ 


    int MAX = 100; 


      


    // Returns count of row wise same elements  


    // in two diagonals of mat[n][n] 


    static int countCommon(int mat[][], int n) 


    { 


        int res = 0; 


        for (int i = 0; i < n; i++) 


            if (mat[i][i] == mat[i][n - i - 1]) 


                res++; 


        return res; 


    } 


  


    // Driver Code 


    public static void main(String args[])throws IOException 


    { 


        int mat[][] = {{1, 2, 3},  


                       {4, 5, 6}, 


                       {7, 8, 9}}; 


        System.out.println(countCommon(mat, 3)); 


    } 


} 


  


// This code is contributed by Anshika Goyal. 



















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Python3














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# Python3 program to find common  


# elements in two diagonals. 


  


Max = 100


  


# Returns count of row wise same 


# elements in two diagonals of 


# mat[n][n] 


def countCommon(mat, n): 


    res = 0


      


    for i in range(n): 


          


        if mat[i][i] == mat[i][n-i-1] : 


            res = res + 1


    return res      


  


# Driver Code 


mat = [[1, 2, 3], 


       [4, 5, 6], 


       [7, 8, 9]] 


  


print(countCommon(mat, 3)) 


  


# This code is contributed by Anant Agarwal. 



















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C#














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// C# program to find common  


// elements in two diagonals. 


using System; 


  


class GFG { 


      


    // Returns count of row wise same 


    // elements in two diagonals of 


    // mat[n][n] 


    static int countCommon(int [,]mat, int n) 


    { 


        int res = 0; 


          


        for (int i = 0; i < n; i++) 


            if (mat[i,i] == mat[i,n - i - 1]) 


                res++; 


                  


        return res; 


    } 


  


    // Driver Code 


    public static void Main() 


    { 


        int [,]mat = {{1, 2, 3},  


                      {4, 5, 6}, 


                      {7, 8, 9}}; 


        Console.WriteLine(countCommon(mat, 3)); 


    } 


} 


  


// This code is contributed by vt_m. 



















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PHP














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<?php 


// PHP program to find common  


// elements in two diagonals. 


$MAX = 100; 


  


// Returns count of row wise 


// same elements in two  


// diagonals of mat[n][n] 


function countCommon($mat, $n) 


{ 


    global $MAX; 


    $res = 0; 


    for ($i = 0; $i < $n; $i++) 


        if ($mat[$i][$i] == $mat[$i][$n - $i - 1]) 


            $res++; 


    return $res; 


} 


  


// Driver Code 


$mat = array(array(1, 2, 3),  


             array(4, 5, 6), 


             array(7, 8, 9)); 


echo countCommon($mat, 3); 


  


// This code is contributed by aj_36 


?> 



















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Output :


  1  



This article is contributed by Himanshu Ranjan. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.


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Improved By :  vt_m, jit_t


					
		

    Article Tags : 
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