[SCOI2010]连续攻击游戏

#include<cstdio>
#include<cctype>
#include<algorithm>
inline int getint() {
    register char ch;
    while(!isdigit(ch=getchar()));
    register int x=ch^'0';
    while(isdigit(ch=getchar())) x=(((x<<2)+x)<<1)+(ch^'0');
    return x;
}
const int M=10001;
int anc[M];
bool vis[M];
int find(const int &x) {
    return x==anc[x]?x:anc[x]=find(anc[x]);
}
int main() {
    for(register int i=0;i<M;i++) anc[i]=i;
    for(register int n=getint();n;n--) {
        int x=find(getint()-1),y=find(getint()-1);
        if(x==y) {
            vis[x]=true;
        } else {
            if(x>y) std::swap(x,y);
            vis[vis[x]?y:x]=true;
            anc[x]=y;
        }
    }
    for(register int i=0;i<M;i++) {
        if(!vis[i]) {
            printf("%d\n",i);
            return 0;
        }
    }
}