[BOJ] 2668번 - 숫자고르기

https://www.acmicpc.net/problem/2668

2668번: 숫자고르기

---

sol) dfs

#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <cstring>
using namespace std;
int v[101];
int n;
int ans;
int check[200];
set <int> s;
void dfs(int depth, int start, int a)
{
    while (1)
    {
        if (v[depth] != -1 && v[depth] == start)
        {
            for (int i = 1; i <= n; i++)
            {
                if (check[i] == a) {
                    s.insert(i);
                    v[i] = -1;
                }
            }
            break;
        }
        if (v[depth] != -1 && check[v[depth]] != a)
        {
            check[v[depth]] = a;
            depth = v[depth];
        }
        else
            break;
    }
}
int main(void)
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int a = 1;
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> v[i];
    for (int i = 1; i <= n; i++)
    {
        check[i] = a;
        dfs(i, i, a);
        a++;
    }
    cout << s.size() << '\n';
    for (auto i : s)
        cout << i << '\n';
}