LeetCode/LeetCode/cpp/lc_0018.cpp at master · duycc/LeetCode · GitHub

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/**
 * @file     lc_0018.cpp
 * @brief    https://leetcode-cn.com/problems/4sum/
 * @author   YongDu
 * @date     2021-09-08
 */
class Solution {
  public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        std::vector<std::vector<int>> result;
        std::sort(nums.begin(), nums.end());
        for (int i = 0; i < nums.size(); ++i) {
            if (nums[i] > target && nums[i] >= 0) {
                break;
            }
            if (i > 0 && nums[i] == nums[i - 1]) {
                continue;
            }
            for (int j = i + 1; j < nums.size(); ++j) {
                if (nums[i] + nums[j] > target && nums[i] + nums[j] >= 0) {
                    break;
                }
                if (j > i + 1 && nums[j] == nums[j - 1]) {
                    continue;
                }
                int left = j + 1;
                int right = nums.size() - 1;
                while (left < right) {
                    long long currSum = (long long)nums[i] + nums[j] + nums[left] + nums[right];
                    if (currSum > target) {
                        right--;
                    } else if (currSum < target) {
                        left++;
                    } else {
                        result.emplace_back(std::vector<int>{nums[i], nums[j], nums[left], nums[right]});
                        while (left < right && nums[left] == nums[left + 1]) {
                            left++;
                        }
                        while (left < right && nums[right] == nums[right - 1]) {
                            right--;
                        }
                        left++;
                        right--;
                    }
                }
            }
        }
        return result;
    }
};