用Java解决岛屿数量问题

Question

岛屿数量
给你一个由 '1'（陆地）和 '0'（水）组成的的二维网格，请你计算网格中岛屿的数量。

岛屿总是被水包围，并且每座岛屿只能由水平方向和/或竖直方向上相邻的陆地连接形成。

此外，你可以假设该网格的四条边均被水包围。

示例 1：

输入：grid = [
["1","1","1","1","0"],
["1","1","0","1","0"],
["1","1","0","0","0"],
["0","0","0","0","0"]
]
输出：1
示例 2：

输入：grid = [
["1","1","0","0","0"],
["1","1","0","0","0"],
["0","0","1","0","0"],
["0","0","0","1","1"]
]
输出：3
提示：

m == grid.length
n == grid[i].length
1 <= m, n <= 300
grid[i][j] 的值为 '0' 或 '1'

Answer 1

class Solution {
    public int numIslands(char[][] grid) {
        int islandNum = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                if (grid[i][j] == '1') {
                    infect(grid, i, j);
                    islandNum++;
                }
            }
        }
        return islandNum;
    }
    public void infect(char[][] grid, int i, int j) {
        if (i < 0 || i >= grid.length ||
                j < 0 || j >= grid[0].length || grid[i][j] != '1') {
            return;
        }
        grid[i][j] = '2';
        infect(grid, i + 1, j);
        infect(grid, i - 1, j);
        infect(grid, i, j + 1);
        infect(grid, i, j - 1);
    }
}