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].

排列组合的问题，不用考虑是否发生重复的情况，代码如下：

1 class Solution { 2 public: 3     vector
     
      
       > permute(vector
       
        & nums) { 4         memset(mark, 0, sizeof(mark)); 5         memset(cdds, 0, sizeof(cdds)); 6         dfs(0, nums.size(), nums); 7         return ret; 8     } 9 10     void dfs(int dep, int maxDep, vector
        
          & nums)11     {12         if(dep == maxDep){13             tmp.clear();14             for(int i = 0;i < maxDep; ++i)15                 tmp.push_back(cdds[i]);16             ret.push_back(tmp);17         }else{18             for(int i = 0; i < maxDep; ++i){19                 if(!mark[i]){20                     mark[i] = true;21                     cdds[dep] = nums[i];22                     dfs(dep + 1, maxDep, nums);23                     mark[i] = false;24                 }25             }26         }27     }29 private:30     int cdds[100];31     bool mark[100];32     vector
         
           tmp;33     vector
          
           
            > ret;34 35 };