Problem
Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
The solution set must not contain duplicate quadruplets.
Example:
Given array nums = [1, 0, -1, 0, -2, 2], and target = 0. A solution set is: [ [-1, 0, 0, 1], [-2, -1, 1, 2], [-2, 0, 0, 2] ] Solution
/** * @param {number[]} nums * @param {number} target * @return {number[][]} */ var fourSum = function(nums, target) { if (nums.length < 4) return []; var len = nums.length; var res = []; var l = 0; var r = 0; var sum = 0; nums.sort((a, b) => (a - b)); for (var 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 - 1] + nums[len - 2] + nums[len - 3] < target) continue; for (var 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 - 1] + nums[len - 2] < target) continue; l = j + 1; r = len - 1; while (l < r) { sum = nums[i] + nums[j] + nums[l] + nums[r]; if (sum < target) { l++; } else if (sum > target) { r--; } else { res.push([nums[i], nums[j], nums[l], nums[r]]); while (l < r && nums[l] === nums[l + 1]) l++; while (l < r && nums[r] === nums[r - 1]) r--; l++; r--; } } } } return res; }; Explain:
see 3Sum.
Complexity:
- Time complexity : O(n^3).
- Space complexity : O(1).