POJ1182 食物链 【并查集变种】

挺简单的

N个元素扩展为 3*N个

i-A i-B i-C

A吃B吃C吃A

挑战程序设计的89面

#include <cstdio>#include <cstdlib>#include <iostream>#include <cstring>#include <cmath>using namespace std;int N,K;const int MAX_N=333333;//并查集int par[MAX_N];int rank[MAX_N];//树的高度void init(int n){for(int i=0;i<n;i++){par[i]=i;rank[i]=0;}}int find(int x)//{if(par[x]==x)return x;elsereturn par[x]=find(par[x]);}//合并x和y所属的集合void unite(int x,int y){x=find(x);y=find(y);if(x==y)return;if(rank[x]<rank[y])par[x]=y;else{par[y]=x;if(rank[x]==rank[y])rank[x]++;}}//判断x和y是否同属于一个集合bool same(int x, int y){return find(x)==find(y);}int main(){#ifndef ONLINE_JUDGEfreopen("G:/1.txt","r",stdin);freopen("G:/2.txt","w",stdout);#endif    scanf("%d%d",&N,&K);init(3*N);int kind,a,b;int ans=0;for(int i=0;i<K;i++){scanf("%d%d%d",&kind,&a,&b);int x=a-1;int y=b-1;if(x<0||x>=N||y<0||y>=N){ans++;continue;}if(kind==1){if(same(x,y+N)||same(x,y+2*N)){ans++;continue;}unite(x,y);unite(x+N,y+N);unite(x+2*N,y+2*N);}else{if(same(x,y)||same(x+N,y+N)||same(x+2*N,y+2*N)||same(x,y+2*N)){ans++;continue;}unite(x,y+N);unite(x+N,y+2*N);unite(x+2*N,y);}}printf("%d\n",ans);return 0;}