leetcode--Permutations(打印所有排列)

Problem Description:

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].

思路分析：

利用递归性质，先固定一个数，然后对剩下的数进行排列，直到剩下最后一个数，形成一个排列，循环将当前数字与剩下的数依次交换后再递归，直到递归结束。

代码如下：

class Solution {
public:

    void swap(int &a,int &b)
    {
        int temp=a;
        a=b;
        b=temp;
    }
    
    void permutations(vector
  
    num,int begin,vector
   
     &permutation,vector
    
      > &res) { if(begin==num.size()) { res.push_back(permutation); return; } for(vector
     
      ::size_type index=begin;index!=num.size();++index) { swap(num[begin],num[index]); permutation.push_back(num[begin]); permutations(num,begin+1,permutation,res); permutation.pop_back(); swap(num[begin],num[index]); } } vector
      
        > permute(vector
       
         &num) { vector
        
          > res; if(num.empty()) return res; vector
         
           permutation; permutations(num,0,permutation,res); return res; } };