Given a binary tree, return the?preorder?traversal of its nodes' values.

Example:

Input:?[1,null,2,3]1\2/3Output:?[1,2,3]

Follow up:?Recursive solution is trivial, could you do it iteratively?

def preOrderTraversal(self,root):# 遞歸res = []def dfs(self,root):if not root:returnres.append(root.val)dfs(root.left)dfs(root.right)dfs(root)return res# 非遞歸stack = [root]res = []while stack:node = stack.pop()res.append(node.val)if node.right:stack.append(node.right)if node.left:stack.append(node.left)return res

?

總結

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