跟 食物链 完全一样

并查集即可。。

1 #include 
      
        2 #include 
       
         3 using namespace std; 4 #define N 100100 5  6 int rank[3*N+100]; 7 int par[3*N+100]; 8 int n,m; 9 10 void init(int n) {11     for (int i=1;i<=n;i++) {12         rank[i]=0;13         par[i]=i;14     }15 }16 17 int find(int x) {18     if (par[x]==x) return x;19     return par[x]=find(par[x]);20 }21 22 void unite(int x,int y) {23     x=find(x);  y=find(y);24     if (x==y) return;25     if (rank[x]
        
         N || x<1 || y>N || y<1) continue;44         if (k==1) {45             if (x==y) {46                 ans++;47                 continue;48             }49             if (same(x,y+N) || same(x,y+2*N))50                 continue;51             else  {52                 unite(x,y);53                 unite(x+N,y+N);54                 unite(x+2*N,y+2*N);55                 ans++;56             }57         }58         else {59             if (x==y) continue;60             if (same(x,y) || same(x,y+2*N))61                 continue;62             else {63                 unite(x,y+N);64                 unite(x+N,y+2*N);65                 unite(x+2*N,y);66                 ans++;67             }68         }69     }70     printf("%d",ans);71 }