46 Permutations

Medium

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

Example:

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Input: [1,2,3]
Output:
[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]
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class Solution {
public:
    vector<vector<int>>res;
    vector<bool> vis;//表示这个解遇到过了;
    
    void backtrace(const vector<int>&nums,vector<int>&track,int index){
        //index记录vis的编号;
        if(index==nums.size()){
            res.push_back(track);
            return;
        }
        for(int i=0;i<nums.size();i++){
            if(vis[i]){
                ;
            }else{
                //没有访问过;
                vis[i]=true;
                track.push_back(nums[i]);
                backtrace(nums,track,index+1);
                track.pop_back();
                vis[i]=false;
                
            }
        }
    }
    vector<vector<int>> permute(vector<int>& nums) {
        res.clear();
        if(nums.size()==0){
            return res;
        }
        vis = vector<bool>(nums.size(), false);
        vector<int> track;
        backtrace(nums,track,0);
        return res;
        
        
    }
};