LeetCode 15. 3Sum

Two Pointer

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Notice that the solution set must not contain duplicate triplets.

Example 1:

Input: nums = [-1,0,1,2,-1,-4]
Output: [[-1,-1,2],[-1,0,1]]

Example 2:

Input: nums = []
Output: []

Example 3:

Input: nums = [0]
Output: []

Constraints:

• 0 <= nums.length <= 3000

• -10^5 <= nums[i] <= 10^5

Solution:

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