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网格（Grid）

2022-07-07 21:50:00 【Yake1965】

Grid

[463. 岛屿的周长](https://leetcode.cn/problems/island-perimeter/)
[200. 岛屿数量](https://leetcode.cn/problems/number-of-islands/)
[1905. 统计子岛屿](https://leetcode.cn/problems/count-sub-islands/)
[695. 岛屿的最大面积](https://leetcode.cn/problems/max-area-of-island/)
[1254. 统计封闭岛屿的数目](https://leetcode.cn/problems/number-of-closed-islands/)
[827. 最大人工岛](https://leetcode.cn/problems/making-a-large-island/)
[1568. 使陆地分离的最少天数](https://leetcode.cn/problems/minimum-number-of-days-to-disconnect-island/)
[417. 太平洋大西洋水流问题](https://leetcode.cn/problems/pacific-atlantic-water-flow/)
[剑指 Offer II 105. 岛屿的最大面积](https://leetcode.cn/problems/ZL6zAn/)

463. 岛屿的周长

class Solution {
    
    int[] a = {
    0, 1, 0, -1}, b = {
    1, 0, -1, 0};
    public int islandPerimeter(int[][] grid) {
    
        int n = grid.length, m = grid[0].length, ans = 0;
        for (int i = 0; i < n; ++i) {
    
            for (int j = 0; j < m; ++j) {
    
                if (grid[i][j] == 0) continue;               
                for (int k = 0; k < 4; k++) {
    
                    int x = i + a[k], y = j + b[k];
                    if (x < 0 || x >= n || y < 0 || y >= m || grid[x][y] == 0) ans += 1; 
                }
            }
        }
        return ans;
    }
}

200. 岛屿数量

class Solution {
    
    int m, n;
    public int numIslands(char[][] grid) {
    
        m = grid.length;
        n = grid[0].length;
        int ans = 0;
        for (int i = 0; i < m; i++) {
    
            for (int j = 0; j < n; j++) {
    
                if (grid[i][j] == '1') {
    
                    ans++;
                    dfs(grid, i, j);
                }
            }
        }
        return ans;
    }
    void dfs(char[][] grid, int i, int j) {
    
        if (i < 0 || j < 0 || i >= m || j >= n || grid[i][j] == '0') return;
        grid[i][j] = '0';
        dfs(grid, i - 1, j);
        dfs(grid, i + 1, j);
        dfs(grid, i, j - 1);
        dfs(grid, i, j + 1);
    }
}