Number of Islands II

 1 public class Solution {
 2     private int count;
 3     private int[] parent;
 4     public List<Integer> numIslands2(int m, int n, int[][] positions) {
 5         List<Integer> result = new ArrayList<>();
 6         if (positions.length == 0) {
 7             return result;
 8         }
 9         parent = new int[m*n];
10         int[][] islands = new int[m][n];
11         count = 0;
12         
13         for (int i = 0; i < parent.length; i++) {
14             parent[i] = i;
15         }
16 
17         for (int[] position : positions) {
18             int x = position[0];
19             int y = position[1];
20             islands[x][y] = 1;
21             count++;
22             
23             if (x > 0 && islands[x - 1][y] == 1) {
24                 union(x*n + y, (x - 1)*n + y);
25             }
26             
27             if (x < m - 1 && islands[x + 1][y] == 1) {
28                 union(x*n + y, (x + 1)*n + y);
29             }
30             
31             if (y > 0 && islands[x][y - 1] == 1) {
32                 union(x*n + y, x * n + y - 1);
33             }
34             
35             if (y < n - 1 && islands[x][y + 1] == 1) {
36                 union(x*n + y, x * n + y + 1);
37             }
38             result.add(count);
39         }
40         return result;
41     }
42     
43     private void union(int a, int b) {
44         int indexA = findParent(a);
45         int indexB = findParent(b);
46         if (indexA != indexB) {
47             count--;
48             parent[indexA] = parent[indexB];
49         }
50     }
51     
52     private int findParent(int x) {
53         while (x != parent[x]) {
54             parent[x] = parent[parent[x]];
55             x = parent[x];
56         }
57         return x;
58     }
59 }
posted on 2016-07-06 06:18 keepshuatishuati 阅读(129) 评论(0) 编辑收藏举报