Description
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: 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] ]
思路
题意：给出一串整数值，输出a + b + c = 0的方案
题解：求三个数之和为0的方案则可以转换成求两个数为0的方案。
public class Solution {
//72ms
public List<List<Integer>> threeSum(int[] nums) {
List<List<Integer>>res = new ArrayList<>();
int len = nums.length;
Arrays.sort(nums);
for (int i = 0;i < len - 2;i++){
int sum = -nums[i];
int left = i + 1,right = len - 1;
while (left < right){
if (nums[left] + nums[right] < sum){
left++;
} else if (nums[left] + nums[right] > sum){
right--;
} else{
res.add(Arrays.asList(nums[i],nums[left],nums[right]));
while (++left < right && nums[left] == nums[left - 1]){}
while (--right > left && nums[right] == nums[right + 1]){}
}
}
while (i + 1 < len - 2 && nums[i + 1] == nums[i]){
i++;
}
}
return res;
}
}