Permutations

Permutations

  

Given a collection of 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].

思路：运用递归求解，第一位和后面的每一位替换，递归到最后一位。

class Solution {public:    void permutation(vector<vector<int>> &ret, vector<int> &nums,int pStr,int pbegin)    {        if(pbegin == nums.size())        ret.push_back(nums);        else        {            for(int i = pbegin;i < nums.size();++i)            {                int tmp = nums[pbegin];                nums[pbegin] = nums[i];                nums[i] = tmp;                permutation(ret,nums,pStr,pbegin+1);                tmp = nums[pbegin];                nums[pbegin] = nums[i];                nums[i] = tmp;            }        }    }    vector<vector<int>> permute(vector<int>& nums) {        vector<vector<int>> ret;         if(0 == nums.size())         return ret;         permutation(ret,nums,0,0);         return ret;    }};