LA 3644 X-Plosives

题目：X-Plosives

思路：并查集。只有当存在环时，才有可能爆炸。

代码：#include <cstdio>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <cstring>
#include <map>
using namespace std;

int f[1000000];

int find(int x){
if(f[x]==-1) return x;
return f[x]=find(f[x]);
}

int main() {

int x,y,ans=0;
memset(f,-1,sizeof(f));
while(~scanf("%d",&x)){
if(x==-1){
printf("%d\n",ans);
ans=0;
memset(f,-1,sizeof(f));
continue;
}
scanf("%d",&y);
int fa1=find(x),fa2=find(y);
if(fa1==fa2) ans++;
else f[fa1]=fa2;
}

return 0;
}