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145. binary tree postorder traversal 解法

admin 11月 12, 2020 0

145. Binary Tree Postorder Traversal

Difficulty: Hard

Given a binary tree, return the postorder traversal of its nodes’ values.

Example:

Input: [1,null,2,3]
   1
    
     2
    /
   3

Output: [3,2,1]

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

解法

class :
    def postorderTraversal(self, root: TreeNode) -> List[int]:
        ans = []
        if root == None:
            return []
        st = [root]
        while len(st) != 0:
            node = st.pop()
            ans.append(node.val)
            if node.left:
                st.append(node.left)
            if node.right:
                st.append(node.right)
        return ans[::-1]