200. Number of Islands

题目

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.

解法

/**
 * @param {character[][]} grid
 * @return {number}
 */

var grid = [
    ["1","1","1"],
    ["0","1","0"],
    ["1","1","1"]];


  
var numIslands = function(grid) {
    const row = grid.length;
    const col = grid[0].length;
    let islands = 0;

    for ( let i = 0; i < row; i++) {
        for (let j = 0; j < col; j++) {
            if (grid[i][j] == 1) {
                console.log('add', i , j)
                islands++
                grid[i][j] = 2;
                
                bsfIslands(grid, row, col, i, j);
            }
        }
    }  
    return islands; 
};

var bsfIslands = function(grid, row, col, i, j) {
    // 遍历上面的
    if (i - 1 >= 0 && grid[i-1][j] == 1) { 
        grid[i-1][j] = 2;
        bsfIslands(grid, row, col, i-1, j);
    }

    // 遍历右边的
    if (j + 1 < col && grid[i][j+1] == 1) {
        grid[i][j + 1] = 2;
        bsfIslands(grid, row, col, i, j+1);
    } 
    // 遍历下面的
    if (i + 1 < row && grid[i+1][j] == 1) {
        grid[i+1][j] = 2;
        bsfIslands(grid, row, col, i + 1, j);
    } 
    // 遍历左边
    if (j - 1 >= 0 && grid[i][j-1] == 1) { 
        // console.log('遍历左边', grid[i][j-1] )
        grid[i][j-1] = 2;
        bsfIslands(grid, row, col, i, j - 1);
    }
    return;  
}


console.log(numIslands(grid))