LeetCode-in-Java

3239. Minimum Number of Flips to Make Binary Grid Palindromic I

Medium

You are given an m x n binary matrix grid.

A row or column is considered palindromic if its values read the same forward and backward.

You can flip any number of cells in grid from 0 to 1, or from 1 to 0.

Return the minimum number of cells that need to be flipped to make either all rows palindromic or all columns palindromic.

Example 1:

Input: grid = [[1,0,0],[0,0,0],[0,0,1]]

Output: 2

Explanation:

Flipping the highlighted cells makes all the rows palindromic.

Example 2:

Input: grid = [[0,1],[0,1],[0,0]]

Output: 1

Explanation:

Flipping the highlighted cell makes all the columns palindromic.

Example 3:

Input: grid = [[1],[0]]

Output: 0

Explanation:

All rows are already palindromic.

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m * n <= 2 * 105
• 0 <= grid[i][j] <= 1

Solution

public class Solution {
    public int minFlips(int[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        int rowFlips = 0;
        for (int i = 0; i < m / 2; i++) {
            for (int j = 0; j < n; j++) {
                int sum = grid[i][j] + grid[m - 1 - i][j];
                rowFlips += Math.min(sum, 2 - sum);
            }
        }
        int columnFlips = 0;
        for (int j = 0; j < n / 2; j++) {
            for (int[] ints : grid) {
                int sum = ints[j] + ints[n - 1 - j];
                columnFlips += Math.min(sum, 2 - sum);
            }
        }
        return Math.min(rowFlips, columnFlips);
    }
}

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