Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such
that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
The solution set must not contain duplicate quadruplets.
Example:
Given array nums = [1, 0, -1, 0, -2, 2], and target = 0.
A solution set is:
[
[-1, 0, 0, 1],
[-2, -1, 1, 2],
[-2, 0, 0, 2]
]
public List<List<Integer>> fourSum(int[] nums, int target) {
List<List<Integer>> result = new ArrayList<>();
Arrays.sort(nums);
for(int i = 0; i < nums.length-3; i++) {
if(i > 0 && nums[i] == nums[i-1]) continue;
for(int j = i+1; j < nums.length-2; j++) {
if(j > i+1 && nums[j] == nums[j-1]) continue;
int t = target - nums[i] - nums[j];
int l = j + 1, r = nums.length - 1;
while(l < r) {
if(l > j+1 && nums[l] == nums[l-1]) {
l++;
continue;
}
int sum = nums[l] + nums[r];
if(sum < t) l++;
else if(sum > t) r--;
else {
result.add(Arrays.asList(new Integer[]{nums[i],nums[j],nums[l],nums[r]}));
l++;
r--;
}
}
}
}
return result;
}