LA 3644 X-Plosives

 1 //#define LOCAL
 2 #include <cstdio>
 3 
 4 const int maxn = 100000 + 10;
 5 int parent[maxn];
 6 
 7 int GetParent(int a) { return parent[a] == a ? a : parent[a] = GetParent(parent[a]); }
 8 
 9 int main(void)
10 {
11     #ifdef LOCAL
12         freopen("3644in.txt", "r", stdin);
13     #endif
14 
15     int x, y;
16     while(scanf("%d", &x) == 1)
17     {
18         for(int i = 0; i < maxn; ++i)    parent[i] = i;
19         int cnt = 0;
20         while(~x)
21         {
22             scanf("%d", &y);
23             x = GetParent(x); y = GetParent(y);
24             if(x == y)    ++cnt;
25             else        parent[x] = y;
26             scanf("%d", &x);
27         }
28         printf("%d\n", cnt);
29     }
30     return 0;
31 }