110. Balanced Binary Tree

memo.md

@@ -2,12 +2,94 @@
 
 ## アプローチ
 
+* highed-balancedかどうかを判定する
+* 左の高さと右の高さがわかれば少なくとも今注目しているノードに対してはhighed-balancedかどうかを判定できる
+* 全てのノードでそれをやればいい
+* 再帰でやる
+* 右と左の高さを計算したいから, 各再帰での役割は高さを出すことにしたい
+* O(N)
+* 2:17
+
 ## Code1-1
 
+* AC: 10:13
+
+```python
+class Solution:
+    def isBalanced(self, root: Optional[TreeNode]) -> bool:
+        if not root:
+            return True
+
+        def is_balanced_helper(root: TreeNode) -> tuple[int, bool]:
+            left_height = 0
+            left_balanced = True
+            if root.left is not None:
+                left_height, left_balanced = is_balanced_helper(root.left)
+
+            right_height = 0
+            right_balanced = True
+            if root.right is not None:
+                right_height, right_balanced = is_balanced_helper(root.right)
+
+            balanced = left_balanced and right_balanced and abs(left_height - right_height) <= 1
+
+            return max(left_height, right_height) + 1, balanced
+
+        return is_balanced_helper(root)[1]
+
+```
+
 # Step2
 
 ## Code2-1
 
+```python
+class Solution:
+    def isBalanced(self, root: Optional[TreeNode]) -> bool:
+        if not root:
+            return True
+
+        def is_balanced_helper(root: TreeNode) -> tuple[int, bool]:
+            left_height = 0
+            left_balanced = True
+            if root.left is not None:
+                left_height, left_balanced = is_balanced_helper(root.left)
+
+            right_height = 0
+            right_balanced = True
+            if root.right is not None:
+                right_height, right_balanced = is_balanced_helper(root.right)
+
+            balanced = left_balanced and right_balanced and abs(left_height - right_height) <= 1
+
+            return max(left_height, right_height) + 1, balanced
+
+        return is_balanced_helper(root)[1]
+
+```
+
 # Step3
 
 ## Code3-1
+
+* 2:44
+* 1:29
+* 1:00
+
+```python
+class Solution:
+    def isBalanced(self, root: Optional[TreeNode]) -> bool:
+        def is_balanced_helper(root: TreeNode | None) -> tuple[int, bool]:
+            if root is None:
+                return 1, True
+
+            left_height, left_balanced = is_balanced_helper(root.left)
+            right_height, right_balanced = is_balanced_helper(root.right)
+
+            balanced = left_balanced and right_balanced and abs(left_height - right_height) <= 1
+
+            return max(left_height, right_height) + 1, balanced
+
+        return is_balanced_helper(root)[1]
+
+```