确定比赛名次 最简单的拓朴排序

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stack>
using namespace std;

int N, M, dp[510], visit[510];

int map[510][510];
 
int main( )
{
    int i, j, a, b, t, flag, k;
  while (scanf("%d%d", &N, &M) != EOF) {
        flag = 0;
        k = 0;
        stack<int>q;
        memset(dp, 0, sizeof(dp));
        memset(visit, 0, sizeof(visit));
        memset(map, 0, sizeof(map));
        for  (i = 1; i <= M; i++) {
            scanf("%d%d", &a, &b);
            if(map[a][b] == 1)
                continue;
            dp[b]++;
            map[a][b] = 1;
        }
        for (i = 1; i <= N; i++)
            if(dp[i] == 0) {
                q.push(i); 
                visit[i] = 1;
                break;
            }
        while (!q.empty( )) {
          t = q.top( );
          if(!flag)
          printf("%d",t),flag = 1;
          else
          printf(" %d",t);
          q.pop();
          for (i = 1; i <= N; i++)
            if(map[t][i] == 1)
                dp[i]--;
          for (i = 1; i <= N; i++)
            if(dp[i] == 0 && !visit[i]) {
                q.push(i);
                visit[i] = 1;
                break;
            }    
        }
        if(flag)
        puts("");
        
    }
     return 0;
}