15. 3Sum

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        vector<vector<int>> res;
        if (nums.size() < 3) return res;
        for (int i = 0; i < nums.size() - 2; i++) {
            if (i > 0 && nums[i] == nums[i-1])  continue;
            int t = -nums[i];
            for (int j = i+1, k = nums.size()-1; j < k; ) {
                if (nums[j] + nums[k] < t || j > i+1 && nums[j] == nums[j-1])
                    j++;
                else if (nums[j] + nums[k] > t || k < nums.size()-1 && nums[k] == nums[k+1])
                    k--;
                else if (nums[j] + nums[k] == t) {
                    vector<int> temp;
                    temp.push_back(nums[i]);
                    temp.push_back(nums[j]);
                    temp.push_back(nums[k]);
                    res.push_back(temp);
                    j++;
                    k--;
                }
            }
        }
        return res;
    }
};