[LeetCode] Permutations

题目描述:

Given a collection of distinct numbers, return all possible permutations.

For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].

解题思路：

递归方法，用一个数组来记录当前元素是否已经被访问

class Solution {
public:
    vector<vector<int>> permute(vector<int>& nums) {
        vector<vector<int>> result;
        vector<int> elem;
        vector<bool> visited(nums.size(), false);
        permute(nums, visited, result, elem);
        return result;
    }
private:
    void permute(const vector<int> &nums, vector<bool> &visited, vector<vector<int>> &result, vector<int> &elem) {
        if (nums.size() == elem.size()) {
            result.push_back(elem);
            return;
        }
        
        for (int i = 0; i < nums.size(); ++i) {
            if (!visited[i]) {
                visited[i] = true;
                elem.push_back(nums[i]);
                permute(nums, visited, result, elem);
                visited[i] = false;
                elem.pop_back();
            }
        }
    }
};