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++
// 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 :
1
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