HDU 3926 Hand in Hand

http://acm.hdu.edu.cn/showproblem.php?pid=3926

题意：一群小孩随机跑动，一声令下就要牵手……就是给你两个图，每个点度数为2，判断两个图是否相等。（每个图只能是链、环）。

题解：使用并查集判断，点数是否在一个集合内，是否成环。然后依据每棵树的节点数数量进行排序，进行判断。之前并查集模板好像有错。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <map>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <numeric>
#include <functional>
#include <set>
#include <fstream>

using namespace std;

const int maxn=10010;

int par[maxn];
int rankh[maxn];
int ISCIRCLE[maxn];
int pos1,pos2;
struct node{
    int rankn,iscircle;
};
node n1[maxn],n2[maxn];

bool cmp(const node& n1,const node& n2)
{
    if(n1.rankn!=n2.rankn) return n1.rankn<n2.rankn;
    if(n1.iscircle<n2.iscircle) return true;
    return false;
}

void init(int n)
{
    memset(ISCIRCLE,0,sizeof(ISCIRCLE));
    for(int i=0;i<=n;i++)
    {
        par[i]=i;
        rankh[i]=1;
    }
}

int find(int x)
{
    if(par[x]==x)
    {
        return x;
    }
    else{
        return par[x]=find(par[x]);
    }
}

void unite(int x,int y)
{
    x=find(x);
    y=find(y);
    if(x==y)
    {
        ISCIRCLE[x]=1;
        return;
    }
    if(rankh[x]<rankh[y])
    {
        par[x]=y;
        rankh[y]+=rankh[x];
    }
    else{
        par[y]=x;
        rankh[x]+=rankh[y];
        //if(rankh[x]==rankh[y]) rankh[x]++;
    }
}

bool judge()
{
    if(pos1!=pos2) return false;
    sort(n1,n1+pos1,cmp);
    sort(n2,n2+pos2,cmp);
    for(int i=0;i<pos1;i++)
    {
        if(n1[i].rankn!=n2[i].rankn) return false;
        if(n1[i].iscircle!=n2[i].iscircle) return false;
    }
    return true;
}

int main()
{
    //freopen("/Users/apple/Desktop/暑假/14(1)/14(1)/in","r",stdin);
    int T;
    scanf("%d",&T);
    int ca=1;
    while(T--)
    {
        printf("Case #%d: ",ca++);
        int N1,M1;
        scanf("%d%d",&N1,&M1);
        int u,v;
        init(N1);
        for(int i=0;i<M1;i++)
        {
            scanf("%d%d",&u,&v);
            unite(u,v);
        }
        pos1=0;
        for(int i=1;i<=N1;i++)
        {
            if(i==find(i))
            {
                n1[pos1].rankn=rankh[i];
                n1[pos1].iscircle=ISCIRCLE[i];
                pos1++;
            }
        }
        int N2,M2;
        scanf("%d%d",&N2,&M2);
        init(N2);
        for(int i=0;i<M2;i++)
        {
            scanf("%d%d",&u,&v);
            unite(u,v);
        }
        if(N1!=N2||M1!=M2)
        {
            puts("NO");
            continue;
        }
        pos2=0;
        for(int i=1;i<=N2;i++)
        {
            if(i==find(i))
            {
                n2[pos2].rankn=rankh[i];
                n2[pos2].iscircle=ISCIRCLE[i];
                pos2++;
            }
        }
        if(judge()) puts("YES");
        else puts("NO");
    }
    return 0;
}