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: 6Â
Explanation:Â
Rotating all the columns of matrix by 1 modifies mat[][] to { {2, 1, 2}, {1, 2, 2}, {1, 1, 2} }.Â
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++
#include <bits/stdc++.h>
using namespace std;
#define N 3
int findMaximumDiagonalSumOMatrixf( int A[][N])
{
int maxDiagonalSum = INT_MIN;
for ( int i = 0; i < N; i++) {
int curr = 0;
for ( int j = 0; j < N; j++) {
curr += A[j][(i + j) % N];
}
maxDiagonalSum = max(maxDiagonalSum,
curr);
}
for ( int i = 0; i < N; i++) {
int curr = 0;
for ( int j = 0; j < N; j++) {
curr += A[(i + j) % N][j];
}
maxDiagonalSum = max(maxDiagonalSum,
curr);
}
return maxDiagonalSum;
}
int main()
{
int mat[N][N] = { { 1, 1, 2 },
{ 2, 1, 2 },
{ 1, 2, 2 } };
cout<< findMaximumDiagonalSumOMatrixf(mat);
return 0;
}
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Time Complexity: O(N2)Â
Auxiliary Space: O(1)
Please refer complete article on Maximize sum of diagonal of a matrix by rotating all rows or all columns for more details!
Last Updated :
27 Jan, 2022
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