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Minimum operations required to set all elements of binary matrix in C++
Problem statement
Given a binary matrix of N rows and M columns. The operation allowed on the matrix is to choose any index (x, y) and toggle all the elements between the rectangle having top-left as (0, 0) and bottom-right as (x-1, y-1). Toggling the element means changing 1 to 0 and 0 to 1. The task is to find minimum operations required to make set all the elements of the matrix i.e make all elements as 1.
Example
If input matrix is {0, 0, 0, 1, 1}
{0, 0, 0, 1, 1}
{0, 0, 0, 1, 1}
{1, 1, 1, 1, 1}
{1, 1, 1, 1, 1}
Then answer is 1In one move, choose (3, 3) to make the whole matrix consisting of only 1s.
Algorithm
The idea is to start from the end point (N – 1, M – 1) and traverse the matrix in reverse order. Whenever we encounter a cell which has a value of 0, flip it
Example
#include <iostream>
#define ROWS 5
#define COLS 5
using namespace std;
int getMinOperations(bool arr[ROWS][COLS]) {
int ans = 0;
for (int i = ROWS - 1; i >= 0; i--){
for (int j = COLS - 1; j >= 0; j--){
if(arr[i][j] == 0){
ans++;
for (int k = 0; k <= i; k++){
for (int h = 0; h <= j; h++){
if (arr[k][h] == 1)
arr[k][h] = 0;
else
arr[k][h] = 1;
}
}
}
}
}
return ans;
}
int main() {
bool mat[ROWS][COLS] = {
0, 0, 1, 1, 1,
0, 0, 0, 1, 1,
0, 0, 0, 1, 1,
1, 1, 1, 1, 1,
1, 1, 1, 1, 1
};
cout << "Minimum required operations = " << getMinOperations(mat) << endl;
return 0;
}Output
When you compile and execute above program. It generates following output −
Minimum required operations = 3
Updated on: 22-Nov-2019
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