BestCoder25 1001.Harry and Magical Computer（hdu 5154） 解题报告

  1 /*
  2 #include <iostream>
  3 #include <cstring>
  4 #include <cstdio>
  5 using namespace std;
  6 
  7 const int maxn = 100 + 10;
  8 int set[maxn];
  9 
 10 int find(int x)
 11 {
 12     while (x != set[x])
 13         x = set[x];
 14     return x;
 15 }
 16 
 17 void merge(int x, int y)
 18 {
 19     int fx = find(x);
 20     int fy = find(y);
 21     printf("fx = %d, fy = %d\n", fx, fy);
 22     if (fx != fy)
 23     {
 24         set[fx] = fy;
 25         printf("set[%d] = %d\n", fx, fy);
 26     }
 27 }
 28 
 29 int main()
 30 {
 31     #ifndef ONLINE_JUDGE
 32         freopen("in.txt", "r", stdin);
 33     #endif // ONLINE_JUDGE
 34 
 35     int n, m, from, to;
 36     while (scanf("%d%d", &n, &m) != EOF)
 37     {
 38         memset(set, 0, sizeof(set));
 39         for (int i = 1; i <= n; i++)
 40             set[i] = i;
 41         for (int i = 0; i < m; i++)
 42         {
 43             scanf("%d%d", &from, &to);
 44             merge(to, from);
 45         }
 46 
 47         for (int i = 1; i <= n; i++)
 48         {
 49             printf("set[%d] = %d\n", i, set[i]);
 50 
 51         }
 52 
 53         puts("");
 54     }
 55     return 0;
 56 }
 57 
 58 */
 59 
 60 #include <iostream>
 61 #include <cstring>
 62 #include <cstdio>
 63 using namespace std;
 64 
 65 const int maxn = 100 + 10;
 66 int map[maxn][maxn];
 67 int in[maxn];
 68 int n, m;
 69 
 70 int main()
 71 {
 72     #ifndef ONLINE_JUDGE
 73         freopen("in.txt", "r", stdin);
 74     #endif // ONLINE_JUDGE
 75     int from, to;
 76     while (scanf("%d%d", &n, &m) != EOF) {
 77         memset(map, 0, sizeof(map));
 78         memset(in, 0, sizeof(in));
 79         for (int i = 0; i < m; i++) {
 80             scanf("%d%d", &to, &from);
 81             if (!map[from][to]) {
 82                 map[from][to] = 1;
 83                 in[to]++;         // 入度
 84             }
 85         }
 86         for (int i = 1; i <= n; i++) {
 87             for (int j = 1; j <= n; j++) {
 88                 if (!in[j]) {
 89                     in[j] = -1;
 90                     for (int k = 1; k <= n; k++) {
 91                         if (map[j][k]) {
 92                             map[j][k] = 0;
 93                             in[k]--;
 94                         }
 95                     }
 96                     break;
 97                 }
 98             }
 99         }
100         
101         bool flag = true;
102         for (int i = 1; i <= n; i++) {
103             if (in[i] != -1) {
104                 flag = false;
105                 break;
106             }
107         }
108         printf("%s\n", flag ? "YES" : "NO");
109     }
110     return 0;
111 }