这里保证1.元素a不会重复。2.所有解都是有序的。3.b和c元素不重复。所以解不会重复。

class Solution {
public:vector<vector<int>> threeSum(vector<int>& nums) {std::vector<std::vector<int>> result;if (nums.size() < 3) return result;std::sort(nums.begin(), nums.end());for (int i = 0; i < nums.size() - 2; ++i) {if (i > 0 && nums[i] == nums[i-1]) continue;  // Skip duplicate numbersint left = i + 1;int right = nums.size() - 1;while (left < right) {int sum = nums[i] + nums[left] + nums[right];if (sum == 0) {result.push_back({nums[i], nums[left], nums[right]});while (left < right && nums[left] == nums[left+1]) left++;  // Skip duplicateswhile (left < right && nums[right] == nums[right-1]) right--;  // Skip duplicatesleft++;right--;} else if (sum < 0) {left++;} else {right--;}}}return result;}
};