【HDOJ】1325 Is It A Tree?

并查集。需要考虑入度。

 #include <stdio.h>
 #include <string.h>

 #define MAXNUM 10005

 int bin[MAXNUM];
 int degree[MAXNUM];
 int nums[MAXNUM];

 int find(int x) {
     int r = x;

     while (bin[r] != r)
         r = bin[r];

     return r;
 }

 int main() {
     int x, y, fx, fy, n, case_n = ;
     int i, flg;

     while () {
         scanf("%d %d", &x, &y);
         if (x< && y<)
             break;
         memset(degree, , sizeof(degree));
         n = ;
         ++case_n;
         if (x== && y==) {
             printf("Case %d is a tree.\n", case_n);
             continue;
         }
         for (i=; i<MAXNUM; ++i)
             bin[i] = i;
         fx = find(x);
         fy = find(y);
         bin[fy] = fx;
         degree[y]++;
         flg = ;
         nums[n++] = x;
         nums[n++] = y;
         while () {
             scanf("%d %d", &x, &y);
             if (x== && y==)
                 break;
             fx = find(x);
             fy = find(y);
             if (fx != fy) {
                 bin[fy] = fx;
                 degree[y]++;
             } else {
                 bin[fy] = fx;
                 degree[y]++;
                 flg = ;
             }
             nums[n++] = x;
             nums[n++] = y;
         }
         fx = find(nums[]);
         for (i=; i<n; ++i) {
             fy = find(nums[i]);
             if (fx != fy) {
                 flg = ;
                 break;
             }
         }
         for (i=; i<n; ++i) {
             if (degree[nums[i]] > ) {
                 flg = ;
                 break;
             }
         }
         if (flg)
             printf("Case %d is a tree.\n", case_n);
         else
             printf("Case %d is not a tree.\n", case_n);
     }

     return ;
 }