Problem P29. [算法课回溯]优美的排列

回溯加上满足优美的排列判断

#include<iostream>
#include<bits/stdc++.h>
#include<cstdio>
#include<string>

using namespace std;

int cnt;

void backTrack(vector<bool>& used, int idx, int n) {
    if (idx > n) {
        cnt++;
        return;
    }
    for (int i = 1; i < n+1; i++) {
        if (used[i] == true && (i%idx == 0 || idx%i == 0)) {
            used[i] = false;
            backTrack(used, idx+1, n);
            // 回溯
            used[i] = true;
        }
    }
}

int main()
{
    int n;
    cin >> n;
    vector<bool> used = vector<bool>(n+1, true);
    backTrack(used, 1, n);
    cout << cnt;
    return 0;
}