LeetCode Permutations

class Solution {
private:
    vector<vector<int> > result;
public:
    vector<vector<int> > permute(vector<int> &num) {
        result.clear();
        dfs(num, 0);
        return result;
    }
    
    void dfs(vector<int>& num, int idx) {
        int tmp;
        int len = num.size();
        if (len == idx + 1) {
            result.push_back(num);
            return;
        }
        for (int i=idx; i<len; i++) {
            tmp = num[idx];
            num[idx] = num[i];
            num[i] = tmp;
            dfs(num, idx + 1);
            tmp = num[idx];
            num[idx] = num[i];
            num[i] = tmp;
        }
    }
};

重复的情况竟然可以，又水了一发