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]
]
排一下序，然后从第一个开始，用两个指针一个指向头一个指向尾，向中间进行遍历，如果遇上一个数字相同就跳到下一个。
vector<vector<int>> threeSum(vector<int>& nums) {
vector<vector<int>> ans;
sort(nums.begin(), nums.end());
for (int i = 0; i < nums.size(); ++i) {
int num = nums[i];
if (num == nums[i - 1] && i > 0)
continue;
int left = i + 1;
int right = nums.size() - 1;
while (left < right) {
//cout << left << " " << right << endl;
if (num + nums[left] + nums[right] < 0) {
left++;
while (nums[left] == nums[left - 1] && left < right)
left++;
} else if (num + nums[left] + nums[right] > 0) {
right--;
while (nums[right] == nums[right + 1] && left < right)
right--;
} else {
ans.push_back({num, nums[left], nums[right]});
left++;
while (nums[left] == nums[left - 1] && left < right)
left++;
}
}
}
return ans;
}
