leetcode problem 3sum

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
         sort(nums.begin(), nums.end());
            vector<vector<int> > validSet;
            for (int i = 0; i < nums.size(); ++i){
                if (i >= 1 && nums[i] == nums[i-1])continue;
                int exp = -nums[i];
                int start = i+1;
                int end = nums.size()-1;
                while (start < end)
                {
                    int sum = nums[start] + nums[end];
                    if (sum == exp){
                        bool good = true;
                        if (validSet.size() > 0){
                            vector<int>& last = validSet[validSet.size()-1];
                            if (nums[i] == last[0] && nums[start] == last[1] && nums[end] == last[2]){
                                good = false;
                            }
                        }
                        if (good){
                            vector<int> res;
                            res.push_back(nums[i]);
                            res.push_back(nums[start]);
                            res.push_back(nums[end]);
                            validSet.push_back(res);
                        }
                        start ++;
                        end --;
                    }
                    else if (sum < exp){
                        start ++;
                    }
                    else {
                        end --;
                    }
                }
            }
            return validSet;
    }
};