题目:
Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
Note:
- Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
- The solution set must not contain duplicate triplets.
For example, given array S = {-1 0 1 2 -1 -4}, A solution set is: (-1, 0, 1) (-1, -1, 2)
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代码:
public class Solution {
public List<List<Integer>> threeSum(int[] nums){
int left, right;
int len = nums.length;
List<List<Integer>> res = new ArrayList<List<Integer>> ();
if(nums == null || nums.length < 3)
return res;
Arrays.sort(nums);
for(int i = 0; i < len - 2; i++){
if(i != 0 && nums[i] == nums[i - 1] )
continue;
left = i + 1;
right = len - 1;
while(left < right)
{
if(nums[i] + nums[left] + nums[right] == 0)
{
List<Integer> list = new ArrayList<>();
list.add(nums[i]);
list.add(nums[left]);
list.add(nums[right]);
res.add(list);
left++;
right--;
while(left < right && nums[left] == nums[left-1])
left++;
while(left < right && nums[right] == nums[right+1])
right--;
}
else if(nums[i] + nums[left] + nums[right] < 0)
left++;
else
right--;
}
}
return res;
}
}