1162. As Far from Land as Possible

Given an n x n grid containing only values 0 and 1, where 0 represents water and 1 represents land, find a water cell such that its distance to the nearest land cell is maximized, and return the distance. If no land or water exists in the grid, return -1.

The distance used in this problem is the Manhattan distance: the distance between two cells (x0, y0) and (x1, y1) is |x0 - x1| + |y0 - y1|.

 

Example 1:

Input: grid = [[1,0,1],[0,0,0],[1,0,1]]
Output: 2
Explanation: The cell (1, 1) is as far as possible from all the land with distance 2.

Example 2:

Input: grid = [[1,0,0],[0,0,0],[0,0,0]]
Output: 4
Explanation: The cell (2, 2) is as far as possible from all the land with distance 4.

 

Constraints:

  • n == grid.length
  • n == grid[i].length
  • 1 <= n <= 100
  • grid[i][j] is 0 or 1

Rust Solution

struct Solution;
use std::collections::VecDeque;

impl Solution {
    fn max_distance(mut grid: Vec<Vec<i32>>) -> i32 {
        let n = grid.len();
        let m = grid[0].len();
        let mut queue: VecDeque<(usize, usize, i32)> = VecDeque::new();
        for i in 0..n {
            for j in 0..m {
                if grid[i][j] == 1 {
                    queue.push_back((i, j, 0));
                }
            }
        }
        let mut res = -1;
        let offsets = [(1, 0), (0, 1), (-1, 0), (0, -1)];
        while let Some((i, j, d)) = queue.pop_front() {
            for offset in &offsets {
                let i = i as i32 + offset.0;
                let j = j as i32 + offset.1;
                if i >= 0 && j >= 0 && i < n as i32 && j < m as i32 {
                    let i = i as usize;
                    let j = j as usize;
                    if grid[i][j] == 0 {
                        grid[i][j] = 1;
                        res = res.max(d + 1);
                        queue.push_back((i, j, d + 1));
                    }
                }
            }
        }
        res as i32
    }
}

#[test]
fn test() {
    let grid = vec_vec_i32![[1, 0, 1], [0, 0, 0], [1, 0, 1]];
    let res = 2;
    assert_eq!(Solution::max_distance(grid), res);
    let grid = vec_vec_i32![[1, 0, 0], [0, 0, 0], [0, 0, 0]];
    let res = 4;
    assert_eq!(Solution::max_distance(grid), res);
}

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