2668 숫자 고르기

#include <stdio.h>
#include <string.h>
 
using namespace std;
 
int ans[105] = { 0 };
int arr[105] = { 0 };
int visit[105] = { 0 };
 
int start, n;
 
void dfs(int idx);
 
int main() {
    scanf("%d", &n);
 
    for (int i = 1; i <= n; i++) {
        scanf("%d", &arr[i]);
    }
 
    for (int i = 1; i <= n; i++) {
        if (ans[i] == 1)
            continue;
 
        start = i;
        dfs(i);
    }
 
    int v = 0;
    for (int i = 1; i <= n; i++) {
        v += ans[i];
    }
    
    printf("%d\n", v);
    for (int i = 1; i <= n; i++) {
        if (ans[i] == 1)
            printf("%d\n", i);
    }
}
 
void dfs(int idx) {
    if (visit[idx] == 1) {
        if (start == idx) {
            for (int i = 1; i <= n; i++) {
                if (visit[i] == 1) {
                    ans[i] = 1;
                }
            }
        }
        else {
            memset(visit, 0, sizeof(visit));
        }
        return;
    }
    visit[idx]++;
 
    dfs(arr[idx]);
}