leetcode15. 三数之和

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 numbers
        int 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 duplicates
                while (left < right && nums[right] == nums[right-1]) right--;  // Skip duplicates
                left++;
                right--;
            } else if (sum < 0) {
                left++;
            } else {
                right--;
            }
        }
    }

    return result;
    }
};