腾讯//全排列

给定一个没有重复数字的序列，返回其所有可能的全排列。

示例:

输入: [1,2,3]
输出:
[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]

class Solution {
public:
    void permute(vector<int>&nums, vector<vector<int>> &ans, int begin,int end){
        if(begin == end){
            ans.push_back(nums);
            return ;
        }else{
            for(int i = begin; i <= end; i++){
                swap(nums, begin, i);
                permute(nums,ans,begin+1,end);
                swap(nums,begin,i);
            }
        }
    }
    void swap(vector<int> &nums, int k,int i){
        int temp = nums[k];
        nums[k]  = nums[i];
        nums[i] = temp;
    }
    vector<vector<int>> permute(vector<int>& nums) {
        vector<vector<int>> ans;
        int len = nums.size()-1;
        permute(nums, ans, 0, len);
        return ans;
    }
};

class Solution {
public:
    void permute(vector<int>nums, vector<vector<int>>& ans, int begin, int end){
        if(begin > end){
            ans.push_back(nums);
            return;
        }else{
            for(int i = begin; i <= end; i++){
                swap(nums[begin], nums[i]);
                permute(nums, ans, begin+1, end); 
            }
        }
    }
    
  
    
    vector<vector<int>> permute(vector<int>& nums) {
        vector<vector<int>> ans;
        int len = nums.size()-1;
        permute(nums, ans, 0, len);
        return ans;
    }
};