[LeetCode] 18. 4Sum

\(▔▽▔)/

	class Solution {
	public List<List<Integer>> fourSum(int[] nums, int target) {
	List<List<Integer>> result = new ArrayList<>();
	Set<List<Integer>> resultSet = new HashSet<>();
	if (nums == null || nums.length < 4) {
	return result;
	}
	Arrays.sort(nums);
	for (int i = 0; i < nums.length - 3; i++) {
	for (int j = i + 1; j < nums.length - 2; j++) {
	if (j > i + 1 && nums[j] == nums[j - 1]) {
	continue;
	}
	int left = j + 1;
	int right = nums.length - 1;
	while (left < right) {
	int sum = nums[i] + nums[j] + nums[left] + nums[right];
	if (sum == target) {
	resultSet.add(Arrays.asList(nums[i], nums[j], nums[left], nums[right]));
	left++;// Attn!
	right--;
	} else if (sum > target) {
	right--;
	} else {
	left++;
	}
	}
	}
	}
	for (List<Integer> solution : resultSet) {
	result.add(solution);
	}
	return result;
	}
	}

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