1254. Number of Closed Islands

Given a 2D `grid` consists of `0s` (land) and `1s` (water).  An island is a maximal 4-directionally connected group of `0s` and a closed island is an island totally (all left, top, right, bottom) surrounded by `1s.`

Return the number of closed islands.

Example 1:

```Input: grid = [[1,1,1,1,1,1,1,0],[1,0,0,0,0,1,1,0],[1,0,1,0,1,1,1,0],[1,0,0,0,0,1,0,1],[1,1,1,1,1,1,1,0]]
Output: 2
Explanation:
Islands in gray are closed because they are completely surrounded by water (group of 1s).```

Example 2:

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

Example 3:

```Input: grid = [[1,1,1,1,1,1,1],
[1,0,0,0,0,0,1],
[1,0,1,1,1,0,1],
[1,0,1,0,1,0,1],
[1,0,1,1,1,0,1],
[1,0,0,0,0,0,1],
[1,1,1,1,1,1,1]]
Output: 2
```

Constraints:

• `1 <= grid.length, grid[0].length <= 100`
• `0 <= grid[i][j] <=1`

1254. Number of Closed Islands
``````struct Solution;

impl Solution {
fn closed_island(mut grid: Vec<Vec<i32>>) -> i32 {
let mut res = 0;
let n = grid.len();
let m = grid[0].len();
for i in 0..n {
for j in 0..m {
if grid[i][j] == 0 && Self::dfs(i, j, &mut grid, n, m) {
res += 1;
}
}
}
res
}

fn dfs(i: usize, j: usize, grid: &mut Vec<Vec<i32>>, n: usize, m: usize) -> bool {
grid[i][j] = 1;
let top = if i > 0 {
if grid[i - 1][j] == 1 {
true
} else {
Self::dfs(i - 1, j, grid, n, m)
}
} else {
false
};
let left = if j > 0 {
if grid[i][j - 1] == 1 {
true
} else {
Self::dfs(i, j - 1, grid, n, m)
}
} else {
false
};
let bottom = if i + 1 < n {
if grid[i + 1][j] == 1 {
true
} else {
Self::dfs(i + 1, j, grid, n, m)
}
} else {
false
};
let right = if j + 1 < m {
if grid[i][j + 1] == 1 {
true
} else {
Self::dfs(i, j + 1, grid, n, m)
}
} else {
false
};
top && left && bottom && right
}
}

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