Given an array of integers, are there elements , , , and in such that + + + = target? Find all unique quadruplets in the array which gives the sum of target.
Note: The solution set must not contain duplicate quadruplets.
- For example, given array S = [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]
- ]
tag : two points
- public class Solution {
- public List<List<Integer>> fourSum(int[] nums, int target) {
- List<List<Integer>> result = new ArrayList<List<Integer>>();
- if(nums == null || nums.length < 4){
- return result;
- }
- Arrays.sort(nums);
- for(int i = 0; i < nums.length - 3; i++){
- int a = nums[i];
- if(i != 0 && nums[i-1] == nums[i]){
- continue;
- }
- int j;
- for(j = i + 1; j < nums.length - 2; j ++){
- int b = nums[j];
- if(j != i + 1 && nums[j-1] == nums[j] ){
- continue;
- }
- int left = j + 1;
- int right = nums.length - 1;
- while(left < right){
- int sum = a + b + nums[left] + nums[right];
- if(sum == target){
- List<Integer> list = new ArrayList<Integer>();
- list.add(a);
- list.add(b);
- list.add(nums[left]);
- list.add(nums[right]);
- result.add(list);
- left++;
- right--;
- while(left < right && nums[left] == nums[left-1]){
- left++;
- }
- while(left < right && nums[right+1] == nums[right]){
- right--;
- }
- }else if(sum < target){
- left++;
- }else{
- right--;
- }
- }
- }
- }
- return result;
- }
- }
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