HDU - 1116 Play on Words(欧拉图)

有向图是否具有欧拉通路或回路的判定:

欧拉通路:图连通；除2个端点外其余节点入度=出度；1个端点入度比出度大1；一个端点入度比出度小1 或 所有节点入度等于出度

欧拉回路:图连通；所有节点入度等于出度

#include<stdio.h>

#include<string.h>

#define MAX 27

int in[MAX],out[MAX];

int visit[MAX],father[MAX];

int find(int index)

{

    if(index==father[index]) return index;

    else return find(father[index]);

}

int main(void)

{

    int t,n;

    int i,j;

    int s,e;

    char str[1001];

    scanf("%d",&t);

    while(t--)

    {

        scanf("%d",&n);

        memset(visit,0,sizeof(visit));

        memset(in,0,sizeof(in));

        memset(out,0,sizeof(out));

        for(i=0;i<MAX;i++) father[i]=i;



        for(i=0;i<n;i++){

            scanf("%s",str);

            int len=strlen(str);

            s=str[0]-'a',e=str[len-1]-'a';

            father[s]=father[e]=find(s);

            visit[s]=visit[e]=1;

            out[s]++;in[e]++;

        }

        //判断改图是否连通

        int r=0;

        for(i=0;i<MAX;i++){

            if(visit[i]&&i==father[i]) r++;

        }

        if(r>1){ //aba abc

            printf("The door cannot be opened.\n"); continue;

        }



        int x,y,z,h;

        x=y=z=h=0;

        for(i=0;i<MAX;i++){

            if(visit[i]){

                if(out[i]-in[i]==1==1) x++;

                else if(in[i]-out[i]==1)y++;

                else if(in[i]==out[i]) z++;

                else h++;

            }

        }

        if(h==0&&((x==1&&y==1)||(x==0||y==0))) printf("Ordering is possible.\n");

        else printf("The door cannot be opened.\n");



    }

    return 0;

}