Minimum depth of binary tree

arai60/minimum_depth_of_binary_tree/phase1.py

@@ -0,0 +1,18 @@
+class Solution:
+    def minDepth(self, root: Optional[TreeNode]) -> int:
+        # 幅優先で良い
+        minimum_depth = 0
+        queue = deque([(root, 0)])
+        while queue:
+            node, depth = queue.popleft()
+            if not node:
+                minimum_depth = depth
+                break
+            if node.right and node.left:
+                queue.append((node.right, depth + 1))
+                queue.append((node.left, depth + 1))
+            elif node.right is not None:
+                queue.append((node.right, depth + 1))
+            else:
+                queue.append((node.left, depth + 1))
+        return minimum_depth

arai60/minimum_depth_of_binary_tree/phase2.py

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+"""
+Reference:
+fhiyo: https://github.com/fhiyo/leetcode/pull/24/files
+rossy0213: https://github.com/rossy0213/leetcode/pull/11/files
+hayashi-ay: https://github.com/hayashi-ay/leetcode/pull/26
+shining-ai: https://github.com/shining-ai/leetcode/pull/22/files
+"""
+
+# if文を簡潔に改善, 枝葉の判定をnode.right, node.leftどちらもnoneの時にすることに
+class Solution:
+    def minDepth(self, root: Optional[TreeNode]) -> int:
+        if not root:
+            return 0
+        # 幅優先で良い
+        minimum_depth = 0
+        queue = deque([(root, 1)])
+        while queue:
+            node, depth = queue.popleft()
+            if not node.right and not node.left:
+                # 枝葉
+                minimum_depth = depth
+                break # ここで早期returnしてしまって, while文を抜けたらraise Exception("unreachable")する手もある(hayashi-ayさん)
+            if node.right:
+                queue.append((node.right, depth + 1))
+            if node.left:
+                queue.append((node.left, depth + 1))
+
+        return minimum_depth
+
+# 再帰で深さ優先探索
+class Solution:
+    def minDepth(self, root: Optional[TreeNode]) -> int:
+        if not root:
+            return 0
+        if not root.right:
+            return self.minDepth(root.left) + 1
+        if not root.left:
+            return self.minDepth(root.right) + 1
+        return min(self.minDepth(root.left), self.minDepth(root.right)) + 1

arai60/minimum_depth_of_binary_tree/phase3.py

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+class Solution:
+    def minDepth(self, root: Optional[TreeNode]) -> int:
+        if not root:
+            return 0
+        minimum_depth = 0
+        queue = deque([(root, 1)])
+        while queue:
+            node, depth = queue.popleft()
+            if not node.left and not node.right:
+                minimum_depth = depth
+                break
+            if node.left:
+                queue.append((node.left, depth + 1))
+            if node.right:
+                queue.append((node.right, depth + 1))
+        return minimum_depth