这也能算hard题？？利用哈希的思想轻松搞定。

#include <stdio.h>

int main(int argc, char *argv[]) {
  int count = 0;
  int res[1000];
  memset(res, -1, sizeof(res));
  scanf("%d", &count);
  while (--count >= 0) {
    int tmp;
    scanf("%d", &tmp);
    res[tmp] = tmp;
  }
  for (int i = 0; i < 1000; ++i) {
    if (res[i] != -1) {
      printf("%d\n", res[i]);
    }
  }
  return 0;
}