易爆物（X-Plosives ）基础并查集

 #include <iostream>
 #include <algorithm>
 using namespace std;
 const int maxn =  + ;
 int fa[maxn];

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

 int main(){
     int a, b;
     while (cin >> a){

         //init
         for (int i = ; i < maxn; i++)
             fa[i] = i;
         int ans = ;
         while (a != -){
             cin >> b;
             a = Find(a);
             b = Find(b);
             if (a == b)
                 ans++;
             else
                 fa[b] = a;
             cin >> a;
         }
         cout << ans << endl;
     }
     //system("pause");
     return ;
 }