README_EN.md

200. Number of Islands

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Description

Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.

An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

 

Example 1:

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

Example 2:

Input: grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
Output: 3

 

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 300
• grid[i][j] is '0' or '1'.

Solutions

Python3

Java

TypeScript

function numIslands(grid: string[][]): number {
    let m = grid.length, n = grid[0].length;
    let ans = 0;
    for (let i = 0; i < m; ++i) {
        for (let j = 0; j < n; ++j) {
            if (grid[i][j] == '1') {
                dfs(grid, i, j);
                ++ans;
            }
        }
    }
    return ans;
};

function dfs(grid: string[][], i: number, j: number) {
    let m = grid.length, n = grid[0].length;
    if (i < 0 || i > m - 1 || j < 0 || j > n - 1 || grid[i][j] == '0') {
        return;
    }
    grid[i][j] = '0';
    for (let [dx, dy] of [[0, 1], [0, -1], [1, 0], [-1, 0]]) {
        let x = i + dx, y = j + dy;
        dfs(grid, x, y);
    }
}

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