[mandoolala] WEEK 3 solutions

3sum/mandoolala.py

@@ -0,0 +1,21 @@
+from typing import List
+
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        answer = set()
+        sorted_nums = sorted(nums)
+
+        for i in range(len(nums) - 2):
+            low, high = i + 1, len(nums) - 1
+            while low < high:
+                three_sum = sorted_nums[i] + sorted_nums[low] + sorted_nums[high]
+                if three_sum == 0:
+                    answer.add((sorted_nums[i], sorted_nums[low], sorted_nums[high]))
+                    low += 1
+                    high -= 1
+                elif three_sum < 0:
+                    low += 1
+                elif three_sum > 0:
+                    high -= 1
+        return list(answer)
+

climbing-stairs/mandoolala.py

@@ -0,0 +1,12 @@
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        if n == 1:
+            return 1
+        if n == 2:
+            return 2
+        dp = [0]*n
+        dp[0] = 1
+        dp[1] = 2
+        for i in range(2, n):
+            dp[i] = dp[i-1] + dp[i-2]
+        return dp[n-1]

product-of-array-except-self/mandoolala.py

@@ -0,0 +1,14 @@
+from typing import List
+
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        answer = [1] * len(nums)
+        left_product = 1
+        for i in range(len(nums) - 1):
+            left_product *= nums[i]
+            answer[i + 1] *= left_product
+        right_product = 1
+        for i in range(len(nums) - 1, 0, -1):
+            right_product *= nums[i]
+            answer[i - 1] *= right_product
+        return answer

valid-anagram/mandoolala.py

@@ -0,0 +1,3 @@
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        return sorted(s) == sorted(t)

validate-binary-search-tree/mandoolala.py

@@ -0,0 +1,20 @@
+from typing import Optional
+
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+class Solution:
+    def isValidBST(self, root: Optional[TreeNode]) -> bool:
+        def traverse(node, low, high):
+            if not node:
+                return True
+            if not (low < node.val < high):
+                return False
+            return traverse(node.left, low, node.val) and traverse(node.right, node.val, high)
+
+        return traverse(root, float("-inf"), float("inf"))