47. Permutations II (Medium)

1.問題

• 給予一個重複數字的集合, 回傳所有可能的排列組合

2.想法

• Recursive + back tracking

• 與46.Permutations相同, 但是如果傳入的是重覆的數字則不加入排列而且數列必須先排序

3.程式碼

class Solution {
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        vector<vector<int>> res;
        vector<int> record;
        vector<bool> used(nums.size(), false);
        sort(nums.begin(), nums.end());
        helper(res, nums, record, used);
        return res;
    }
private:
    void helper(vector<vector<int>>& res, vector<int>& nums, vector<int>& record, vector<bool>& used) {
        if (record.size() == nums.size()) {
            res.push_back(record);
            return;
        }
        for (int i = 0 ; i < nums.size(); i++) {
            if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false) {
                continue;
            }
            if (!used[i]) {
                used[i] = true;
                record.push_back(nums[i]);
                helper(res, nums, record, used);
                record.pop_back();
                used[i] = false;
            }
        }
    }
};

4.Performance