# LeetCode 0331 - Verify Preorder Serialization of a Binary Tree

# Verify Preorder Serialization of a Binary Tree

## Desicription

One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node’s value. If it is a null node, we record using a sentinel value such as #.

1 | _9_ |

For example, the above binary tree can be serialized to the string “9,3,4,#,#,1,#,#,2,#,6,#,#”, where # represents a null node.

Given a string of comma separated values, verify whether it is a correct preorder traversal serialization of a binary tree. Find an algorithm without reconstructing the tree.

Each comma separated value in the string must be either an integer or a character ‘#’ representing null pointer.

You may assume that the input format is always valid, for example it could never contain two consecutive commas such as “1,,3”.

**Example 1:**

1 | Input: "9,3,4,#,#,1,#,#,2,#,6,#,#" |

**Example 2:**

1 | Input: "1,#" |

**Example 3:**

1 | Input: "9,#,#,1" |

## Solution

1 | class Solution { |