hdoj1232 畅通工程（并查集）

题目链接

http://acm.hdu.edu.cn/showproblem.php?pid=1232

思路

使用并查集求解。

代码

 #include <iostream>
 #include <cstring>
 #include <cstdio>
 using namespace std;

 const int N =  + ;
 int p[N];

 void make_set(int n)
 {
     for (int i = ; i <= n; i++)
         p[i] = -;
 }

 int find_root(int i)
 {
     if (p[i] == -)
         return i;
     else
     {
         int t = find_root(p[i]);    //路径压缩
         p[i] = t;
         return t;
     }
 }

 void union_set(int a, int b)
 {
     int ra = find_root(a);
     int rb = find_root(b);
     if (ra != rb)
         p[ra] = rb;

 }

 int main()
 {
     //freopen("hdoj1232.txt", "r", stdin);
     int n, m;
     while (scanf("%d%d", &n, &m) ==  && n)
     {
         make_set(n);
         int a, b;
         for (int i = ; i < m; i++)
         {
             scanf("%d%d", &a, &b);
             union_set(a, b);
         }
         int ans = ;
         for (int i = ;i <= n;i++)
             if (p[i] == -) ans++;
         printf("%d\n", ans - );
     }
     return ;
 }