LeetCode-200-岛屿数量
200. 岛屿数量
难度中等1203收藏分享切换为英文接收动态反馈
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'
1
所到之处infect
成2,增加一个岛
class Solution {
public static int numIslands(char[][] m) {
if (m == null || m.length == 0 || m[0] == null || m[0].length == 0) {
return 0;
}
int N = m.length;
int M = m[0].length;
int res = 0;
for (int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
if (m[i][j] == '1') {
res++;
infect(m, i, j, N, M);
}
}
}
return res;
}
// 目前来到m[i][j], 经历上下左右的感染过程
public static void infect(char[][] m, int i, int j, int N, int M) {
if (i < 0 || i >= N || j < 0 || j >= M || m[i][j] != '1') {
return;
}
m[i][j] = '2';
infect(m, i + 1, j, N, M);
infect(m, i - 1, j, N, M);
infect(m, i, j + 1, N, M);
infect(m, i, j - 1, N, M);
}
}