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package two_pointers;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

/**

* Created by gouthamvidyapradhan on 29/03/2017. Given an array S of n integers, are there elements

* a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array

* which gives the sum of target.

*

* <p>Note: The solution set must not contain duplicate quadruplets.

*

* <p>For example, given array S = [1, 0, -1, 0, -2, 2], and target = 0.

*

* <p>A solution set is: [ [-1, 0, 0, 1], [-2, -1, 1, 2], [-2, 0, 0, 2] ]

*/

public class FourSum {

/**

* Main method

*

* @param args

* @throws Exception

*/

public static void main(String[] args) throws Exception {

int[] nums = {1, 0, -1, 0, -2, 2};

System.out.println(new FourSum().fourSum(nums, 0));

}

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

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

if (nums.length < 4) return result;

Arrays.sort(nums);

for (int i = 0; i < nums.length - 3; i++) {

if (i == 0 || nums[i] != nums[i - 1]) {

for (int j = i + 1; j < nums.length - 2; j++) {

if (j == i + 1 || nums[j] != nums[j - 1]) {

int k = j + 1, l = nums.length - 1;

while (k < l) {

if (k != j + 1 && nums[k] == nums[k + 1]) {

k++;

continue;

}

int sum = nums[i] + nums[j] + nums[k] + nums[l];

if (sum == target) {

result.add(Arrays.asList(nums[i], nums[j], nums[k], nums[l]));

k++;

l--;

} else if (sum < target) {

k++;

} else {

l--;

}

}

}

}

}

}

return result;

}

}