HDU1116(欧拉回路+并查集)

来源：互联网发布：淘宝双十一抽奖在哪里编辑：程序博客网时间：2024/05/16 06:51

先用并查集来判断图是否连通，然后再根据欧拉回路的出度和入度的性质来判断是否为欧拉回路。

关键是建边，我们可以把字符串看成是一条边，首字母为出发点，尾字母为目的点，建边。

#include <stdio.h>#include <string.h>#include <string>#include <iostream>#include <algorithm>#include <vector>#include <math.h>#include <map>#include <queue>#include <stack>#include <set>#define M 100000+5#define LL long long#define Ld __int64#define eps 0.00001#define INF 999999999#define MOD 112233#define MAX 26#define PI acos(-1.0)using namespace std;int father[M];int into[M],out[M];set<int> s;int find(int x){    if(x!=father[x])        father[x]=find(father[x]);    return father[x];}void merge(int x,int y){    int fx=find(x);    int fy=find(y);    if(fx!=fy)        father[fx]=fy;}void init(){    for(int i=0;i<M;i++)    {        into[i]=0;        out[i]=0;        father[i]=i;    }    s.clear();}int main(){    int t;    char ch[1005];    scanf("%d",&t);    while(t--)    {        int n;        init();        scanf("%d",&n);        getchar();        for(int i=1;i<=n;i++)        {            scanf("%s",ch);            int a=ch[0]-'a'+1;            int l=strlen(ch);            int b=ch[l-1]-'a'+1;            into[b]++;            out[a]++;            int x=find(a);            int y=find(b);            if(x!=y)                merge(x,y);            s.insert(a);            s.insert(b);        }        int num=0;        set<int>::iterator it;        for(it=s.begin();it!=s.end();it++)        {            if(father[*it]==*it && (into[*it] || out[*it]))                num++;        }        if(num!=1)            printf("The door cannot be opened.\n");        else        {            int f1=0,f2=0,f3=0;            for(it=s.begin();it!=s.end();it++)            {                int p=*it;                if((into[p]-out[p])==1)                    f1++;                if((out[p]-into[p])==1)                    f2++;                if(into[p]==out[p])                    f3++;            }            if(f1==1 && f2==1 && (f1+f2+f3)==(s.size()))                printf("Ordering is possible.\n");            else if(f1==0 && f2==0 && f3==s.size())                printf("Ordering is possible.\n");            else                printf("The door cannot be opened.\n");        }    }    return 0;}

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