[devyejin] WEEK 04 solutions

maximum-depth-of-binary-tree/devyejin.py

@@ -0,0 +1,12 @@
+# 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 maxDepth(self, root: Optional[TreeNode]) -> int:
+        if not root:
+            return 0
+
+        return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1

maximum-subarray/devyejin.py

@@ -1,10 +1,11 @@
 class Solution:
     def maxSubArray(self, nums: list[int]) -> int:
-        dp = [0] * len(nums)
-        dp[0] = nums[0]
+        current_sum = nums[0]
+        max_sum = nums[0]
 
         for i in range(1, len(nums)):
-            dp[i] = max(nums[i], dp[i - 1] + nums[i])
+            current_sum = max(nums[i], current_sum + nums[i])
+            max_sum = max(current_sum, max_sum)
 
-        return max(dp)
+        return max_sum
 

merge-two-sorted-lists/devyejin.py

@@ -0,0 +1,30 @@
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+"""
+time : O(m+n)
+space : O(1)
+"""
+
+
+class Solution:
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+        dummy = ListNode(None)
+
+        node = dummy
+
+        while list1 and list2:
+            if list1.val <= list2.val:
+                node.next = list1
+                list1 = list1.next
+            else:
+                node.next = list2
+                list2 = list2.next
+            node = node.next
+        node.next = list1 or list2
+
+        return dummy.next