【Arai60】26問目 102. Binary Tree Level Order Traversal

arai60/21-29_Tree_BT_BST/26_102_Binary Tree Level Order Traversal/level_1.py

@@ -0,0 +1,18 @@
+# BFSで解く
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        node_queue = deque([root])
+        level_order = []
+        while node_queue:
+            node_num = len(node_queue)
+            nodes = []
+            for _ in range(node_num):
+                node = node_queue.popleft()
+                if not node:
+                    continue
+                nodes.append(node.val)
+                node_queue.append(node.left)
+                node_queue.append(node.right)
+            if nodes:
+                level_order.append(nodes)
+        return level_order

arai60/21-29_Tree_BT_BST/26_102_Binary Tree Level Order Traversal/level_2.py

@@ -0,0 +1,40 @@
+# BFSで解く
+# queueにNoneが入らないように修正
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        if not root:
+            return []
+        node_queue = deque([root])
+        level_order = []
+        while node_queue:
+            num_nodes_in_level = len(node_queue)
+            nodes_in_level = []
+            for _ in range(num_nodes_in_level):
+                node = node_queue.popleft()
+                nodes_in_level.append(node.val)
+                if node.left:
+                    node_queue.append(node.left)
+                if node.right:
+                    node_queue.append(node.right)
+            level_order.append(nodes_in_level)
+        return level_order
+
+
+# DFSで解く
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        if not root:
+            return []
+        level_order = []
+
+        def build_level_order(node, level):
+            while len(level_order) - 1 < level:
+                level_order.append([])
+            level_order[level].append(node.val)
+            if node.left:
+                build_level_order(node.left, level + 1)
+            if node.right:
+                build_level_order(node.right, level + 1)
+
+        build_level_order(root, 0)
+        return level_order

arai60/21-29_Tree_BT_BST/26_102_Binary Tree Level Order Traversal/level_3.py

@@ -0,0 +1,19 @@
+# BFS
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        if not root:
+            return []
+        node_queue = deque([root])
+        level_order = []
+        while node_queue:
+            queue_length = len(node_queue)
+            nodes = []
+            for _ in range(queue_length):
+                node = node_queue.popleft()
+                nodes.append(node.val)
+                if node.left:
+                    node_queue.append(node.left)
+                if node.right:
+                    node_queue.append(node.right)
+            level_order.append(nodes)
+        return level_order

arai60/21-29_Tree_BT_BST/26_102_Binary Tree Level Order Traversal/level_4.py

@@ -0,0 +1,21 @@
+# BFS
+# queueの中身の個数でレベルを判定していた部分を修正(current_queue, next_queueを使うように修正)
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        if not root:
+            return []
+        level_order = []
+        current_queue = deque([root])
+        while current_queue:
+            values_in_level = []
+            next_queue = deque()
+            while current_queue:
+                node = current_queue.popleft()
+                values_in_level.append(node.val)
+                if node.left:
+                    next_queue.append(node.left)
+                if node.right:
+                    next_queue.append(node.right)
+            level_order.append(values_in_level)
+            current_queue = next_queue
+        return level_order