穷举vs暴搜vs深搜vs回溯vs剪枝系列一＞优美的排列

private int count;
    private boolean[] check;
    public int countArrangement(int n) {
        check = new boolean[n+1];
        dfs(n,1);
        return count;
    } 

    private void dfs(int n, int pos){
        if(pos == n+1){
            count++;
            return;
        }

        for(int i = 1; i <= n; i++){
            if(check[i] == false && (i % pos == 0 || pos % i == 0)){
                check[i] = true;
                dfs(n,pos+1);
                check[i] = false;//恢复现场
            }
        }
    }