HDU

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

    }
    return 0;
}