LeetCode-in-Java

3643. Flip Square Submatrix Vertically

Easy

You are given an m x n integer matrix grid, and three integers x, y, and k.

The integers x and y represent the row and column indices of the top-left corner of a square submatrix and the integer k represents the size (side length) of the square submatrix.

Your task is to flip the submatrix by reversing the order of its rows vertically.

Return the updated matrix.

Example 1:

Input: grid = [[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]], x = 1, y = 0, k = 3

Output: [[1,2,3,4],[13,14,15,8],[9,10,11,12],[5,6,7,16]]

Explanation:

The diagram above shows the grid before and after the transformation.

Example 2:

Input: grid = [[3,4,2,3],[2,3,4,2]], x = 0, y = 2, k = 2

Output: [[3,4,4,2],[2,3,2,3]]

Explanation:

The diagram above shows the grid before and after the transformation.

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 50
• 1 <= grid[i][j] <= 100
• 0 <= x < m
• 0 <= y < n
• 1 <= k <= min(m - x, n - y)

Solution

public class Solution {
    public int[][] reverseSubmatrix(int[][] grid, int x, int y, int k) {
        for (int i = 0; i < k / 2; i++) {
            int top = x + i;
            int bottom = x + k - 1 - i;
            for (int col = 0; col < k; col++) {
                int temp = grid[top][y + col];
                grid[top][y + col] = grid[bottom][y + col];
                grid[bottom][y + col] = temp;
            }
        }
        return grid;
    }
}

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