三数之和

给你一个包含n个整数的数组nums，判断nums中是否存在三个元素a，b，c，使得a + b + c = 0？请你找出所有和为0且不重复的三元组。

注意：答案中不可以包含重复的三元组。

  • 示例 1：

    输入：nums = [-1,0,1,2,-1,-4]
输出：[[-1,-1,2],[-1,0,1]]

  • 示例 2：

    输入：nums = []
输出：[]

  • 示例 3：

    输入：nums = [0]
输出：[]

提示：

  • 0 <= nums.length <= 3000
  • -105 <= nums[i] <= 105

Solution

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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        vector<vector<int>> results;
        if (nums.size() < 3) {
            return results;
        }
        sort(nums.begin(), nums.end());
        int len = nums.size();
        for (int i = 0; i < len - 2; ++i) {
            if (i > 0 && nums[i] == nums[i - 1]) {
                continue;
            }
            if (nums[i] + nums[i + 1] + nums[i + 2] > 0) {
                break;
            }
            if (nums[i] + nums[len - 2] + nums[len - 1] < 0) {
                continue;
            }
            int left = i + 1;
            int right = len - 1;
            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                if (sum < 0) {
                    left++;
                } else if ( sum > 0) {
                    right--;
                } else {
                    vector<int> result = {nums[i], nums[left], nums[right]};
                    results.emplace_back(result);
                    while (left < right && nums[left] == nums[left + 1]) {
                        left++;
                    }
                    left++;
                    while (left < right && nums[right - 1] == nums[right]) {
                        right--;
                    }
                    right--;
                }
            }
        }
        return results;
    }
};


int main() {
    vector<int> input;
    vector<vector<int>> results;

    input = {-1,0,1,2,-1,-4};
    results = Solution().threeSum(input); // [[-1,-1,2],[-1,0,1]]
    for (int i = 0; i < results.size(); ++i) {
        for (int j = 0; j < results[i].size(); ++j) {
            std::cout << results[i][j] << " ";
        }
        std::cout << std::endl;
    }
}