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Copy path_18.java
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47 lines (39 loc) · 1.61 KB
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package com.fishercoder.solutions;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**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.
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]
]*/
public class _18 {
public List<List<Integer>> fourSum(int[] nums, int target) {
List<List<Integer>> result = new ArrayList();
if(nums == null || nums.length == 0) return result;
Arrays.sort(nums);
for(int i = 0; i < nums.length -3; i++){
if(i > 0 && nums[i-1] == nums[i]) continue;
for(int j = i+1; j < nums.length-2; j++){
if(j > i+1 && nums[j-1] == nums[j]) continue;
int left = j+1, right = nums.length-1;
while(left < right){
int sum = nums[i] + nums[j] + nums[left] + nums[right];
if(sum == target){
result.add(Arrays.asList(nums[i], nums[j], nums[left], nums[right]));
while(left+1 < right && nums[left] == nums[left+1]) left++;
while(right-1 > left && nums[right] == nums[right-1]) right--;
left++;
right--;
} else if(sum > target) right--;
else left++;
}
}
}
return result;
}
}