[wozlsla] WEEK 04 solutions

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

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+"""
+# Intuition
+트리 전체 순회
+
+# Approach
+-
+
+# Complexity
+time : O(N)
+space : O(N)
+"""
+
+# 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
+
+
+# Stack (top-down)
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+
+        # edge case
+        if not root:
+            return 0
+
+        max_depth = 0
+        stack = [(root, 1)]
+
+        while stack:
+            node, depth = stack.pop()
+
+            max_depth = max(depth, max_depth)  # update depth
+
+            if node.left:
+                stack.append((node.left, depth + 1))
+            if node.right:
+                stack.append((node.right, depth + 1))
+
+        return max_depth
+
+
+""" 재귀 (bottom-top)
+# max_depth : 현재 노드를 기준으로, 좌측과 우측 자식 트리 중 max_depth가 큰 값을 선택해 + 1
+
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+
+        # 기저조건
+        if not root:
+            return 0
+
+        return 1 + max(
+            self.maxDepth(root.left),
+            self.maxDepth(root.right),
+        )
+"""

merge-two-sorted-lists/wozlsla.py

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+"""
+# Intuition
+-
+# Approach
+-
+# Complexity
+time : O(N+M)
+space : O(1) / O(N+M)
+"""
+
+from typing import Optional
+
+
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+class Solution:
+    def mergeTwoLists(
+        self, list1: Optional[ListNode], list2: Optional[ListNode]
+    ) -> Optional[ListNode]:
+
+        dummy = ListNode(None)  # -> None(고정)
+        node = dummy  # -> None(이동)
+
+        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  # (이동)
+
+        # 반복문 종료
+        node.next = list1 or list2
+
+        return dummy.next  # 병합 리스트의 첫 번째 노드를 가리킴
+
+
+# list1: 1 -> 2 -> 4
+list1_node3 = ListNode(4)
+list1_node2 = ListNode(2, list1_node3)
+list1_node1 = ListNode(1, list1_node2)
+
+# list2: 1 -> 3 -> 4
+list2_node3 = ListNode(4)
+list2_node2 = ListNode(3, list2_node3)
+list2_node1 = ListNode(1, list2_node2)
+
+sol = Solution()
+merged_list = sol.mergeTwoLists(list1_node1, list2_node1)
+
+# 결과 출력
+current = merged_list
+result = []
+while current:
+    result.append(current.val)
+    current = current.next
+
+print(result)
+
+
+""" 재귀
+class Solution:
+    def mergeTwoLists(
+        self, list1: Optional[ListNode], list2: Optional[ListNode]
+    ) -> Optional[ListNode]:
+
+        # 기저조건
+        if not (list1 and list2):
+            return list1 or list2
+
+        if list1.val < list2.val:
+            list1.next = self.mergeTwoLists(list1.next, list2)
+            return list1
+        else:
+            list2.next = self.mergeTwoLists(list1, list2.next)
+            return list2
+"""