solution: 3sum

Author: wozlsla

3sum/wozlsla.py

@@ -0,0 +1,96 @@
+"""
+# Intuition
+-
+
+# Approach
+index가 모두 다를것,
+합 = 0 -> -a = b+c
+중복 X -> set : dic와 다르게 가변객체 삽입 X
+Two Pointer -> 정렬된 배열을 활용
+
+# Complexity
+- Time complexity
+  - Brute-force : O(N^3)
+  - Set : O(N^2) - Time Limit Exceeded (memory??)
+  - Two Pointer : O(N^2)
+
+- Space complexity
+  - Brute-force : O(N)
+  - Set : O(N)
+  - Two Pointer : O(1)
+"""
+
+from typing import List
+
+
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+
+        triplets = set()
+        nums.sort()  # O(NlogN), return None
+
+        for i in range(len(nums) - 2):  # O(N)
+            low, high = i + 1, len(nums) - 1
+
+            while low < high:  # O(N)
+                three_sum = nums[i] + nums[low] + nums[high]
+
+                if three_sum < 0:
+                    low += 1
+                elif three_sum > 0:
+                    high -= 1
+                else:
+                    triplets.add((nums[i], nums[low], nums[high]))
+                    low, high = low + 1, high - 1
+
+        return list(triplets)
+
+
+""" Set
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+
+        triplets = set()
+
+        for i in range(len(nums) - 2):
+            seen = set()
+
+            for j in range(i + 1, len(nums)):
+                complement = -(nums[i] + nums[j])
+
+                if complement in seen:
+                    triplets.add(tuple(sorted([nums[i], nums[j], complement])))
+
+                seen.add(nums[j])
+
+        return list(triplets)
+"""
+
+""" Brute-force
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+
+        n = len(nums)
+        result = []
+
+        for i in range(n-2):
+            for j in range(i+1, n-1):
+                for k in range(j+1, n):
+                    if i != j and i != k and j != k:
+                    
+                        if nums[i] + nums[j] + nums[k] == 0:
+                            li = sorted([nums[i], nums[j], nums[k]])
+
+                            if li not in result: # O(L)
+                                result.append(li)
+
+        return result
+"""
+
+nums = [-1, 0, 1, 2, -1, -4]
+sol = Solution()
+
+print(sol.threeSum(nums))
+# [[-1,-1,2],[-1,0,1]]
+
+# print(len({1, 1, 2})) # 2