For this problem, do not forget to skip the duplicates for i. Usually I will do duplication removal for j and k.

Tag it.

 

1 class Solution { 2 public: 3     vector
     
      
        > threeSum(vector
       
         &num) { 4         vector
        
         
           > result; 5         int len = num.size(), i = 0, j = 0, k = 0; 6         if (len < 2) return result; 7         sort(num.begin(), num.end()); 8         for (int i = 0; i < len-2; i++) { 9             if (i > 0 && num[i] == num[i-1]) continue;10             j = i+1, k = len-1;11             while (j < k) {12                 int sum = num[i] + num[j] + num[k];13                 if (sum > 0) k--;14                 else if (sum < 0) j++;15                 else {16                     vector
          
            tmp;17 tmp.push_back(num[i]);18 tmp.push_back(num[j]);19 tmp.push_back(num[k]);20 result.push_back(tmp);21 do{j++;} while (j < k && num[j] == num[j-1]);22 do{k--;} while (j < k && num[k] == num[k+1]);23 }24 }25 }26 return result;27 }28 };