331. Verify Preorder Serialization of a Binary Tree

Loading Question ...

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 #.

     _9_
    /   \
   3     2
  / \   / \
 4   1  #  6
/ \ / \   / \
# # # #   # #

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:
"9,3,4,#,#,1,#,#,2,#,6,#,#"
Return true

Example 2:
"1,#"
Return false

Example 3:
"9,#,#,1"
Return false

Credits:
Special thanks to @dietpepsi for adding this problem and creating all test cases.


Seen this question in a real interview before?  
Yes
No
When did you encounter this question?  
last week
last month
last 3 month
last 6 month
more than 6 months
other
Which company?  
Adobe
Aetion
Affirm
Airbnb
Alation
Alibaba
Amazon
AppDynamics
Apple
Arista
Baidu
Bank of America
BlackRock
Blend Labs
Blizzard
Bloomberg
Booking
Box
Bungie
Capital One
CareerBuilder
Cisco
Citadel
Coinbase
Concur
Conviva
Coupang
Coursera
CreditEase
CVTE
Dell
Deutsche Bank
DoorDash
Dropbox
Duolingo
EasyNet
eBay
Electronic Arts
EMC
Epic Systems
Equinix
Evernote
Expedia
Facebook
FactSet
Fitbit
Flipkart
Fortinet
FourSquare
FreeWheel
GoDaddy
Goldman Sachs
Google
GrabTaxi
Groupon
HBO
Hedvig
HomeAway
HTC
Huawei
Hulu
IBG
IBM
Indeed
InnovatureLabs
Intel
IXL
Jane Street
JPMorgan
Jump Trading
Lending Club
LinkedIn
LiveRamp
Loovee
Marvel
Matlab
McKesson
Microsoft
Morgan Stanley
NetEase
Nintendo
Nutanix
Nvidia
Oracle
Orbitz
Palantir
Paypal
Pinterest
Pocket Gems
Point72
Qualcomm
Qualtrics
Qumulo
Quora
Rackspace
Redfin
Rubrik
Salesforce
Samsung
SAP
ServiceNow
Sina
Snapchat
SoftwareOne
Sony
SoundHound
Square
Sumologic
SurveyMonkey
Symantec
Tableau
Tencent
Tesorio
TinyCo
Tradeshift
TripAdvisor
Twilio
Twitter
Two Sigma
Uber
Veritas
Visa
VMware
Walmart
Wealthfront
Whitepages
Works Applications
Yahoo
Yandex
Yelp
Zappos
Zenefits
Zillow
Zynga
  Send Feedback