hdu1232 畅通工程 基础并查集

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <cstdlib>
 using namespace std;

 #define MAXN 1005
 int n, m;
 int fa[MAXN];    //父节点
 int mark[MAXN];

 void init()
 {
     for (int i = ; i <= n; i++)
     {
         fa[i] = i;
         mark[i] = ;
     }
 }

 int find(int x)
 {
     if (x == fa[x])
         return x;
     else
         return fa[x] = find(fa[x]);
 }

 void set_union(int x, int y)
 {
     int x1 = find(x);
     int y1 = find(y);

     if (x1 == y1)
         return;
     if (mark[x1] < mark[y1])
     {
         fa[x1] = y1;
     }
     else
         fa[y1] = x1;
     if (mark[x1] == mark[y1])
         mark[x1]++;
 }

 int main()
 {
     while (~scanf("%d",&n))
     {
         if (n == )
             break;
         scanf("%d", &m);
         init();
         for (int i = ; i < m; i++)
         {
             int a, b;
             scanf("%d %d", &a, &b);
             set_union(a, b);
         }

         int ans = ;
         for (int i = ; i <= n; i++)
         {
             if (find(i) == i)
                 ans++;
         }
         printf("%d\n", ans - );
     }
     //system("pause");
     return ;
 }