HDU 1116 Play on Words（有向欧拉判断）

题目链接

题意：给出一些单词，问全部单词能否首尾相连

直接 将每一个单词第一个和最后一个字母建立一条有向边，保证除了首尾两个出入度不相等，其他的要保证相等。还有一个条件就是 首尾两个出入度差为1

同时并查集判连通

 #include <iostream>
 #include <cstdio>
 #include <cmath>
 #include <cstring>
 #include <algorithm>
 using namespace std;
 const int Max =  + ;
 struct Node
 {
     int x, y;
 };
 char str[Max];
 Node node[Max];
 int indegree[], outdegree[];
 int father[], vis[];
 int find_father(int x)
 {
     if (x == father[x])
         return x;
     return father[x] = find_father(father[x]);
 }
 int unionset(int x, int y)
 {
     x = find_father(x);
     y = find_father(y);
     if (x == y)
         return false;
     father[y] = x;
     return true;
 }
 int main()
 {
     int T, n;
     scanf("%d", &T);
     while (T--)
     {
         scanf("%d", &n);
         memset(indegree, , sizeof(indegree));
         memset(outdegree, , sizeof(outdegree));
         memset(vis, , sizeof(vis));
         for (int i = ; i < ; i++)
             father[i] = i;
         int setcnt = ;
         for (int i = ; i <= n; i++)
         {
             scanf("%s", str);
             node[i].x = str[] - 'a';
             node[i].y = str[ strlen(str) - ] - 'a';
             indegree[node[i].y]++;
             outdegree[node[i].x]++;
             vis[node[i].x] = ;
             vis[node[i].y] = ;
             if (unionset(node[i].x, node[i].y))
             {
                 setcnt++;
             }
         }
         int numcnt = ;
         for (int i = ; i < ; i++)
         {
             if (vis[i])
                 numcnt++;
         }
         if (setcnt != (numcnt - ))
         {
             printf("The door cannot be opened.\n");
             continue;
         }
         if (n == )
         {
             printf("Ordering is possible.\n");
             continue;
         }
         int x = , y = , z = ;
         for (int i = ; i < ; i++)
         {
             if (vis[i] && indegree[i] != outdegree[i])
             {
                 if (indegree[i] == outdegree[i] + ) //首
                     x++;
                 else if (indegree[i] +  == outdegree[i]) // 尾
                     y++;
                 else
                     z++;
             }
         }
         if (z)
             printf("The door cannot be opened.\n");
         else if ( (x ==  && y == ) || (x ==  && y == ) ) // 出入度不相等 且 差为1， 或者 是环
             printf("Ordering is possible.\n");
         else
             printf("The door cannot be opened.\n");
         /*
         int cnt = 0, sum = 0;
         for (int i = 0; i < 26; i++)
         {
             if (indegree[i] > 0 || outdegree[i] > 0)
             {
                 sum++;
                 if (indegree[i] == outdegree[i])
                     cnt++;
             }
         }
         if (cnt == sum || ( sum > 2 && sum - cnt == 2))
             printf("Ordering is possible.\n");
         else
             printf("The door cannot be opened.\n");
             */
     }
     return ;
 }