4Sum

LEETCODE PROBLEM SOLVING
PROBLEM->4SUM
import java.util.*;

class Solution {

    public List<List<Integer>> fourSum(int[] nums, int target) {

        List<List<Integer>> result = new ArrayList<>();

        Arrays.sort(nums);

        int n = nums.length;

        for (int i = 0; i < n - 3; i++) {
            if (i > 0 && nums[i] == nums[i - 1])
                continue;

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

                int left = j + 1;
                int right = n - 1;

                while (left < right) {

                    long sum = (long) nums[i]
                             + nums[j]
                             + nums[left]
                             + nums[right];

                    if (sum == target) {

                        result.add(Arrays.asList(
                                nums[i],
                                nums[j],
                                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 (sum < target) {

                        left++;

                    }

                    else {

                        right--;
                    }
                }
            }
        }

        return result;
    }
}