POJ 1182 食物链

 1 //并查集加点东西，注意负数
 2 #include<cstdio>
 3 #include<cstring>
 4 using namespace std;
 5 int fa[50500];
 6 int right[50500];
 7 int find(int x){
 8     if(fa[x]==x) return x;
 9     int tmp=fa[x];
10     fa[x]=find(fa[x]);
11     right[x]+=right[tmp];
12     right[x]%=3;
13     return fa[x];
14 }
15 int main()
16 {
17     int n,m,k,a,b;
18     scanf("%d%d",&n,&m);
19     memset(right,0,sizeof(right));
20     for(int i=1;i<=n;i++) fa[i]=i;
21     int ans=0;
22     for(int i=1;i<=m;i++){
23         scanf("%d%d%d",&k,&a,&b);
24         if(a>n||b>n) {ans++;continue;}
25         int x=find(a);
26         int y=find(b);
27         if(k==1){
28             if(x==y){
29                 if(right[a]!=right[b]) ans++;
30             }else
31                   fa[y]=x,
32                   right[y]=(right[a]-right[b]+3)%3; 
33         }else
34             if(x==y){
35               if((right[a]+1)%3!=right[b]) ans++;
36             }else
37                   fa[y]=x,
38                   right[y]=(right[a]-right[b]+3+1)%3; 
39             
40     }
41     printf("%d\n",ans);
42     return 0;
43 }