[LeetCode] Problem 15 - 3Sum

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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.

Example

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:

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[
  [-1, 0, 1],
  [-1, -1, 2]
]

Code

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public List<List<Integer>> threeSum(int[] nums) {
    List<List<Integer>> result = new ArrayList<>();

    Arrays.sort(nums);

    for (int i = 0; i < nums.length - 2; i++) {
        if (i > 0 && nums[i] == nums[i - 1])
            continue;

        twoSum(nums, -nums[i], i + 1, nums.length - 1, result);
    }

    return result;
}

private void twoSum(int[] nums, int target, int left, int right, List<List<Integer>> result) {
    while (left < right) {
        if (nums[left] + nums[right] == target) {
            result.add(Arrays.asList(-target, nums[left], nums[right]));
            left++;
            right--;

            while (left < right && nums[left] == nums[left - 1])
                left++;

            while (left < right && nums[right] == nums[right + 1])
                right--;
        } else if (nums[left] + nums[right] < target)
            left++;
        else
            right--;
    }
}