uva-10129 单词

成语接龙可以抽象为欧拉回路，单词为有向边，词头词尾为节点，用dfs判断是否图是否连通，先判断入度出度，然后dfs，在判断图是否连通。visitedv数组用来区别不存在的点、存在的点和存在且已用dfs访问过的点

#include <cstdio>#include <cstring>#include <vector>#include <queue>#include <iostream>using namespace std;#define DEBUGconst int maxn=1000+5,maxv=26;int n,startcnt,endcnt,startv,endv;char s[maxn];int in[26],out[26],visitedv[26];bool visited[26][26],G[26][26],flag;bool dfs(int u){    visitedv[u]=2;    for(int v=0;v<maxv;v++){        if(G[u][v]&&!visited[u][v]){            visited[u][v]=1;            dfs(v);            // printf("%d %d\n",u,v);        }    }    return true;}int main(){#ifdef DEBUG    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);#endif    int m;    cin>>m;    while(m--){        memset(in,0,sizeof(in));        memset(out,0,sizeof(out));        memset(visited,0,sizeof(visited));        memset(G,0,sizeof(G));        memset(visitedv,0,sizeof(visitedv));        startcnt=0;        endcnt=0;        cin>>n;        while(n--){            cin>>s;            int len=strlen(s);            visitedv[s[0]-'a']=visitedv[s[len]-'a']=1;            G[s[0]-'a'][s[len-1]-'a']=1;            in[s[0]-'a']++;out[s[len-1]-'a']++;        }        flag=1;        for(int i=0;i<26;i++){            if(in[i]!=out[i]){                if(in[i]==out[i]+1)                    startv=i,startcnt++;                else if(in[i]+1==out[i])                    endv=i,endcnt++;                else{flag=0;break;}            }            if(!startcnt&&in[i])                startv=i;        }        if(endcnt>1||startcnt>1)flag=0;        if(!flag){cout<<"The door cannot be opened.\n";continue;}        // printf("startv:%d\n",startv);        // printf("endv:%d\n",endv);        dfs(startv);        flag=1;        for(int i=0;i<26;i++)            if(visitedv[i]==1){flag=0;cout<<"The door cannot be opened.\n";break;}        if(flag)        cout<<"Ordering is possible.\n";    }#ifdef DEBUG    fclose(stdin);    fclose(stdout);#endif    return 0;}