What is the time complexity of LeetCode 331. Verify Preorder Serialization of a Binary Tree?

The Python solution on this page runs in O(n).

What is the space complexity of LeetCode 331. Verify Preorder Serialization of a Binary Tree?

The Python solution on this page uses O(n), where n is the length of the string `preorder` auxiliary space.

Verify Preorder Serialization of a Binary Tree — LeetCode 331 Python Solution

MediumStackTreeStringBinary Tree

Problem: #331
Pattern: Stack
Reading time: 2 min
Source: leetcode.com

The problem

One way to serialize a binary tree is to use preorder traversal. When we encounter a non-null node, we record the node's value.

Example

Input: preorder = "9,3,4,#,#,1,#,#,2,#,6,#,#"
Output: true

Python solution

Python

class Solution:
    def isValidSerialization(self, preorder: str) -> bool:
        stk = []
        for c in preorder.split(","):
            stk.append(c)
            while len(stk) > 2 and stk[-1] == stk[-2] == "#" and stk[-3] != "#":
                stk = stk[:-3]
                stk.append("#")
        return len(stk) == 1 and stk[0] == "#"

Complexity

Measure	Complexity
Time	O(n)
Space	O(n), where n is the length of the string `preorder` auxiliary

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 331. Verify Preorder Serialization of a Binary Tree is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Stack.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 331. Verify Preorder Serialization of a Binary Tree?: LeetCode 331. Verify Preorder Serialization of a Binary Tree is rated Medium on LeetCode.
What is the time complexity of LeetCode 331. Verify Preorder Serialization of a Binary Tree?: The Python solution on this page runs in O(n).
What is the space complexity of LeetCode 331. Verify Preorder Serialization of a Binary Tree?: The Python solution on this page uses O(n), where n is the length of the string `preorder` auxiliary space.
What topics does LeetCode 331. Verify Preorder Serialization of a Binary Tree cover?: LeetCode 331. Verify Preorder Serialization of a Binary Tree is tagged Stack, Tree, String and Binary Tree on LeetCode.