C++ Program to Maximize sum of diagonal of a matrix by rotating all rows or all columns
Given a square matrix, mat[][] of dimensions N * N, the task is find the maximum sum of diagonal elements possible from the given matrix by rotating either all the rows or all the columns of the matrix by a positive integer.
Examples:
Input: mat[][] = { { 1, 1, 2 }, { 2, 1, 2 }, { 1, 2, 2 } }
Output: 6
Explanation:
Rotating all the columns of matrix by 1 modifies mat[][] to { {2, 1, 2}, {1, 2, 2}, {1, 1, 2} }.
Therefore, the sum of diagonal elements of the matrix = 2 + 2 + 2 = 6 which is the maximum possible.Input: A[][] = { { -1, 2 }, { -1, 3 } }
Output: 2
Approach: The idea is to rotate all the rows and columns of the matrix in all possible ways and calculate the maximum sum obtained. Follow the steps to solve the problem:
- Initialize a variable, say maxDiagonalSum to store the maximum possible sum of diagonal elements the matrix by rotating all the rows or columns of the matrix.
- Rotate all the rows of the matrix by a positive integer in the range [0, N - 1] and update the value of maxDiagonalSum.
- Rotate all the columns of the matrix by a positive integer in the range [0, N - 1] and update the value of maxDiagonalSum.
- Finally, print the value of maxDiagonalSum.
Below is the implementation of the above approach:
// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;
#define N 3
// Function to find maximum sum of diagonal elements
// of matrix by rotating either rows or columns
int findMaximumDiagonalSumOMatrixf(int A[][N])
{
// Stores maximum diagonal sum of elements
// of matrix by rotating rows or columns
int maxDiagonalSum = INT_MIN;
// Rotate all the columns by an integer
// in the range [0, N - 1]
for (int i = 0; i < N; i++) {
// Stores sum of diagonal elements
// of the matrix
int curr = 0;
// Calculate sum of diagonal
// elements of the matrix
for (int j = 0; j < N; j++) {
// Update curr
curr += A[j][(i + j) % N];
}
// Update maxDiagonalSum
maxDiagonalSum = max(maxDiagonalSum,
curr);
}
// Rotate all the rows by an integer
// in the range [0, N - 1]
for (int i = 0; i < N; i++) {
// Stores sum of diagonal elements
// of the matrix
int curr = 0;
// Calculate sum of diagonal
// elements of the matrix
for (int j = 0; j < N; j++) {
// Update curr
curr += A[(i + j) % N][j];
}
// Update maxDiagonalSum
maxDiagonalSum = max(maxDiagonalSum,
curr);
}
return maxDiagonalSum;
}
// Driver code
int main()
{
int mat[N][N] = { { 1, 1, 2 },
{ 2, 1, 2 },
{ 1, 2, 2 } };
cout<< findMaximumDiagonalSumOMatrixf(mat);
return 0;
}
Output:
6
Time Complexity: O(N2)
Auxiliary Space: O(1)
