Flip square submatrix vertically

Array Two Pointers Matrix

72.9% acceptance

Feb 25, 2026

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.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn reverse_submatrix(mut grid: Vec<Vec<i32>>, x: i32, y: i32, k: i32) -> Vec<Vec<i32>> {
    let (x, y, k) = (x as usize, y as usize, k as usize);
    // Flip the k x k submatrix at top-left (x, y) by reversing row order
    for col_off in 0..k {
      let col = y + col_off;
      let mut top = x;
      let mut bot = x + k - 1;
      while top < bot {
        let tmp = grid[top][col];
        grid[top][col] = grid[bot][col];
        grid[bot][col] = tmp;
        top += 1;
        bot -= 1;
      }
    }
    grid
  }
}