引爆炸弹 计蒜客 并查集

​​题目链接​​

import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class Main {
  public static int f[];
  public static int find(int x){return x == f[x] ? x : (f[x] = find(f[x]));}//路径压缩 + 查询祖先
  public static void main(String[] args) {
    Scanner cin = new Scanner(System.in);
    int n = cin.nextInt();
    int m = cin.nextInt();
    f = new int[n + m + 2];
    char a[][] = new char[n + 2][m + 2];
    for(int i = 0;i < n;i++)
    {
      String s = cin.next();
      for(int j = 0;j < m;j++)
        a[i][j] = s.charAt(j);
    }
    for(int i = 0;i < n;i++)f[i] = i;
    for(int i = 0;i < m;i++)f[i + n] = i + n;
    int vis[] = new int[n + 2];
    for(int i = 0;i < n;i++)
      for(int j = 0;j < m;j++)
        if(a[i][j] == '1'){
          int x = find(i);
          int y = find(j + n);
          if(x != y)f[x] = y;
        }
    int cnt = 0;
    Set<Integer> s = new HashSet<>();
    for(int i = 0;i < n;i++)
      for(int j = 0;j < m;j++)
        if(a[i][j] == '1'){
          s.add(find(i));//这里一定要注意再次寻找祖先，因为之前并未更新孩子的最终祖先。//
        }
    System.out.println(s.size());
  }
}