本文共 2076 字，大约阅读时间需要 6 分钟。

class Solution {public:	void threeSum(int step, int sum,				  vector
   
    & path, vector
    
     
      >& ans, 				  const vector
      
       & num, vector
       
        & used)	{		if(path.size() == 3)		{			ans.push_back(path);			return;		}		if(step >= num.size()) return;		//1. not choose 		threeSum(step+1, sum, path, ans, num, used);		//2. choose		if(step != 0 && num[step] == num[step-1] && !used[step-1]) return;//avoid same combination		if(path.size() == 2 && sum+num[step] != 0) return;//sum not equal to zero		used[step] = true; path.push_back(num[step]); 		threeSum(step+1, sum+num[step], path, ans, num, used);		used[step] = false; path.pop_back();	}    vector
        
         
           > threeSum(vector
          
            &num) { // Start typing your C/C++ solution below // DO NOT write int main() function if(num.size() == 0) return vector
           
            
              >(); sort(num.begin(), num.end()); vector
             
               path; vector
              
               
                > ans; vector
                
                  used(num.size(), false); threeSum(0, 0, path, ans, num, used); return ans; }};
                
               
              
             
            
           
          
         
        
       
      
     
    
   

second time

class Solution {public:    vector
   
    
      > threeSum(vector
     
       &num) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        sort(num.begin(), num.end());                vector
      
       
         > ans;        for(int i = 0; i < num.size(); ++i)        {            if(i != 0 && num[i] == num[i-1]) continue;            int left = i+1;            int right = num.size()-1;            vector
        
          triplet(3); while(left < right) { int sum = num[left]+num[right]+num[i]; if(sum > 0) right--; else if(sum < 0) left++; else { triplet[0] = num[i], triplet[1] = num[left], triplet[2] = num[right]; ans.push_back(triplet); //break; int oldLeftNum = num[left]; while(left < num.size() && num[left] == oldLeftNum) left++; } } } return ans; }};
        
       
      
     
    
   

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