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.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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++

// 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; 
} 

Java

// 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. 

Python3

# 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. 

C#

// 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. 

PHP

<?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 
?> 

Output :

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.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

PHP

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