题解 | #火眼金睛# C语言

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

typedef struct {
  int id;
  int numAnswers;
  int* answerIds;
} Question;

int main() {
  int N;
  while (scanf("%d", &N) != EOF) {
    int* askId = (int*)malloc(N * sizeof(int));
    int* ansNum = (int*)malloc(N * sizeof(int));
    int** map = (int**)malloc((N + 1) * sizeof(int*));
    for (int i = 0; i <= N; i++) {
      map[i] = (int*)calloc(N + 1, sizeof(int));
    }

    for (int i = 0; i < N; i++) {
      scanf("%d %d", &askId[i], &ansNum[i]);
      for (int j = 0; j < ansNum[i]; j++) {
        int ansId;
        scanf("%d", &ansId);
        map[askId[i]][ansId] = 1;
      }
    }

    int* cheatIds = (int*)calloc(N + 1, sizeof(int));
    int cheatCount = 0;
    for (int i = 0; i <= N; i++) {
      int count = 0;
      for (int j = 0; j <= N; j++) {
        if (map[i][j] == 1 && map[j][i] == 1 && i != j) {
          if (cheatIds[i] != 1) {
            cheatIds[i] = 1;
            count++;
          }
        }
        if (map[i][j] == 1 && i != j && cheatIds[j] == 1) {
          count++;
        }
        if (count >= 2 && cheatIds[i] != 1) {
          cheatIds[i] = 1;
        }
      }
      if (cheatIds[i] == 1) {
        cheatCount++;
      }
    }
    int flag = 0;

    printf("%d\n", cheatCount);
    for (int i = 0; i <= N; i++) {
      if (cheatIds[i] == 1) {
        printf("%d ", i);
        flag = 1;
      }
      if ((i == N) && (flag == 1)) {
        printf("\n");
      }
    }

    free(askId);
    free(ansNum);
    for (int i = 0; i <= N; i++) {
      free(map[i]);
    }
    free(map);
    free(cheatIds);
  }

  return 0;
}