4 sum

0018/4Sum.py

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+# Two Pointers approach
+
+class Solution:
+    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
+
+        def kSum(nums: List[int], target: int, k: int) -> List[List[int]]:
+            res = []
+            if len(nums) == 0 or nums[0] * k > target or target > nums[-1] * k:
+                return res
+            if k == 2:
+                return twoSum(nums, target)
+
+            for i in range(len(nums)):
+                if i == 0 or nums[i - 1] != nums[i]:
+                    for subset in kSum(nums[i + 1:], target - nums[i], k - 1):
+                        res.append([nums[i]] + subset)
+
+            return res
+
+        def twoSum(nums: List[int], target: int) -> List[List[int]]:
+            res = []
+            s = set()
+
+            for i in range(len(nums)):
+                if len(res) == 0 or res[-1][1] != nums[i]:
+                    if target - nums[i] in s:
+                        res.append([target - nums[i], nums[i]])
+                s.add(nums[i])
+
+            return res
+
+        nums.sort()
+        return kSum(nums, target, 4)

0018/README.md

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+# 4Sum
+
+Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:
+
+0 <= a, b, c, d < n
+a, b, c, and d are distinct.
+nums[a] + nums[b] + nums[c] + nums[d] == target
+You may return the answer in any order.
+
+
+
+## Example 1:
+
+Input: nums = [1,0,-1,0,-2,2], 
+
+target = 0
+
+Output: [[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
+
+## Example 2:
+
+Input: nums = [2,2,2,2,2], 
+
+target = 8
+
+Output: [[2,2,2,2]]
+
+
+## Constraints:
+
+1 <= nums.length <= 200
+-109 <= nums[i] <= 109
+-109 <= target <= 109