Miscellany

#include <stdio.h>
#include <stdlib.h>

int main() {
    FILE *fin, *fout;
    fin = fopen("s3.in", "r");
    fout = fopen("s3.out", "w");
    
    int list[10000] = { 0 }; // x must be friends with list[x]
    int nstudents;
    
    fscanf(fin, "%d", &nstudents);
    
    for (; nstudents > 0; nstudents--) {
        int x, y;
        fscanf(fin, "%d %d", &x, &y);
        list[x] = y;
    }
    
    while (1) {
          int from, to;
          fscanf(fin, "%d %d", &from, &to);
          
          if (from == 0 && to == 0)
             break;
          
          int counter = 0, start = from, counting = 1;
          printf("%d %d\n", from, to);
          
          while (1) {
              // printf("%d is friends with %d\n", from, list[from]);
              from = list[from];
              
              if (from == to)
                 counting = 0;
              
              if (from == start) {
                 if (counting == 0)
                    fprintf(fout, "Yes %d\n", counter);
                 else
                     fprintf(fout, "No\n");
                 break;
              }
              
              if (!list[from]) {
                 fprintf(fout, "No\n");
                 break;
              }
              
              if (counting)
                 counter++;
              
          }
          
    }
    
    return 0;
}