Number of enclaves

Array Depth-First Search Breadth-First Search Union-Find Matrix

71.5% acceptance

Feb 25, 2026

4592

You are given an m x n binary matrix grid, where 0 represents a sea cell and 1 represents a land cell. A move consists of walking from one land cell to another adjacent (4-directionally) land cell or walking off the boundary of the grid. Return the number of land cells in grid for which we cannot walk off the boundary of the grid in any number of moves.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn num_enclaves(mut grid: Vec<Vec<i32>>) -> i32 {
    let (m, n) = (grid.len(), grid[0].len());
    fn dfs(g: &mut Vec<Vec<i32>>, r: usize, c: usize) {
      if r >= g.len() || c >= g[0].len() || g[r][c] != 1 { return; }
      g[r][c] = 0;
      if r > 0 { dfs(g, r-1, c); }
      dfs(g, r+1, c); dfs(g, r, c+1);
      if c > 0 { dfs(g, r, c-1); }
    }
    for r in 0..m { dfs(&mut grid, r, 0); dfs(&mut grid, r, n-1); }
    for c in 0..n { dfs(&mut grid, 0, c); dfs(&mut grid, m-1, c); }
    grid.iter().flatten().sum()
  }
}