15. 3Sum

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.

Note:
The solution set must not contain duplicate triplets.

public List<List<Integer>> threeSum(int[] nums) {
    Arrays.sort(nums);
    List<List<Integer>> result = new ArrayList<>();
    for(int i = 0; i < nums.length - 2; i++) {
        if(i > 0 && nums[i] == nums[i-1]) continue; // remove duplicate
        int l = i + 1, r = nums.length-1;
        while(l < r) {
            if(l > i+1 && nums[l] == nums[l-1]) { // remove duplicate
                l++;
                continue;
            }

            if(nums[l] + nums[r] + nums[i] == 0) {
                result.add(new ArrayList<Integer>(Arrays.asList(nums[i], nums[l], nums[r])));
                l++;
                r--;
            } else if(nums[l] + nums[r] + nums[i] < 0) {
                l++;
            } else {
                r--;
            }
        }
    }
    return result;
}