Given an array nums of n integers, are there elements a, b, c in nums 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.
Example:
Given array nums = [-1, 0, 1, 2, -1, -4],
A solution set is:
[
[-1, 0, 1],
[-1, -1, 2]
]
双指针法,先排序,注意去除重复值
public List<List<Integer>> threeSum(int[] nums) {
List<List<Integer>> res = new ArrayList<>();
Arrays.sort(nums);
for(int i = 0; i < nums.length - 2; i++){
int target = -nums[i];
int front = i + 1;
int back = nums.length - 1;
while(front < back){
if(nums[front] + nums[back] < target){
front++;
}
else if(nums[front] + nums[back] > target){
back--;
}
else{
res.add(Arrays.asList(nums[i],nums[front],nums[back]));
while(front < back && nums[front+1] == nums[front]) front++;
while(front < back && nums[back-1] == nums[back]) back--;
front++;
back--;
}
}
while(i+1 < nums.length && nums[i+1] == nums[i]) i++;
}
return res;
}