PAT 乙级 1005 继续(3n+1)猜想

题目链接：https://pintia.cn/problem-sets/994805260223102976/problems/994805320306507776

#include <bits/stdc++.h>
using namespace std;
int main() {
    int n; cin >> n;
    int a[n] = {};
    for (int i = 0; i < n; i++)
        cin >> a[i];
    map<int, bool> vis;
    for (int i = 0; i < n; i++) {
        int x = a[i];
        while (x != 1) {
            if (x & 1) x = (3 * x + 1) / 2;
            else x = x / 2;
            vis[x] = true;
        }
    }
    set<int> ans;
    for (int i = 0; i < n; i++) 
        if (!vis[a[i]])
            ans.insert(a[i]);
    for (auto it = ans.rbegin(); it != ans.rend(); it++)
        cout << *it << " \n"[it == --ans.rend()];
}