洛谷 P2451 [SDOI2005]遗传代码 [并查集]

#include<stdio.h>
int f[1024],cnt[1024],cnt2[1024],size[1024],n,ans;
int findroot(int x){
if(f[x]==x)return x;
return f[x]=findroot(f[x]);
}
int main(){
freopen("pie.in","r",stdin);
freopen("pie.out","w",stdout);
for(int i=1;i<=1000;i++)
f[i]=i,size[i]=1;
scanf("%d",&n);
for(int i=0;i<n;i++){
int l,r;
scanf("%d%d",&l,&r);
cnt[l]--;
cnt[r]++;
int lr=findroot(l);
int rr=findroot(r);
if(lr==rr)continue;
f[lr]=rr;
size[rr]+=size[lr];
size[lr]=0;
}
for(int i=1;i<=1000;i++){
if(cnt[i]<0)continue;
cnt2[findroot(i)]+=cnt[i];
}
for(int i=1;i<=1000;i++){
if(!size[i])continue;
ans+=cnt2[i];
if(size[i]>1&&cnt2[i]==0)ans++;
}
printf("%d\n",ans+n);
return 0;
}