四数之和

给定一个包含n个整数的数组nums和一个目标值target，判断nums中是否存在四个元素a，b，c和d ，使得a + b + c + d的值与target相等？找出所有满足条件且不重复的四元组。

注意：答案中不可以包含重复的四元组。

  • 示例 1：

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

  • 示例 2：

    输入：nums = [], target = 0
输出：[]

提示：

  • 0 <= nums.length <= 200
  • -109 <= nums[i] <= 109
  • -109 <= target <= 109

Solution

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

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> results;
        if (nums.size() < 4) {
            return results;
        }
        sort(nums.begin(), nums.end());
        int len = nums.size();
        for (int i = 0; i < len - 3; ++i) {
            if (i > 0 && nums[i] == nums[i - 1]) {
                continue;
            }
            if (nums[i] + nums[i + 1] + nums[i + 2] + nums[i + 3] > target) {
                break;
            }
            if (nums[i] + nums[len - 3] + nums[len - 2] + nums[len - 1] < target) {
                continue;
            }

            for (int j = i + 1; j < len - 2; ++j) {
                if (j > i + 1 && nums[j] == nums[j - 1]) {
                    continue;
                }
                if (nums[i] + nums[j] + nums[j + 1] + nums[j + 2] > target) {
                    break;
                }
                if (nums[i] + nums[j] + nums[len - 2] + nums[len - 1] < target) {
                    continue;
                }
                int left = j + 1;
                int right = len - 1;
                while (left < right) {
                    int sum = nums[i] + nums[j] + nums[left] + nums[right];
                    if (sum < target) {
                        left++;
                    } else if (sum > target) {
                        right--;
                    } else {
                        vector<int> result = {nums[i], nums[j], 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,-1,0,-2,2};
    results = Solution().fourSum(input, 0); // [[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
    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;
    }
}