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].
Implementation:
C++
// CPP program to find common elements in// two diagonals.#include <iostream>#define MAX 100using 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 Codeint 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 Codemat = [[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?> |
Javascript
<script>// Javascript program to find common elements in// two diagonals.let MAX = 100;// Returns count of row wise same// elements in two diagonals of// mat[n][n]function countCommon(mat, n){ let res = 0; for (let i = 0; i < n; i++) if (mat[i][i] == mat[i][n - i - 1]) res++; return res;}// Driver Code let mat = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]; document.write(countCommon(mat, 3));// This code is contributed by subham348.</script> |
Output
1
Time Complexity: O(n).
Auxiliary Space: O(1).
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