?
Solved

map in C++ v/s HashMap in Java

Posted on 2011-03-01
7
Medium Priority
?
796 Views
Last Modified: 2012-05-11
Could you tell me if the time complexity of operations with a map in C++ and HashMap in Java are the same?
IF not, please tell me the time complexity of operations such as Insert/Delete/Search in a map in C++.

Thanks!
0
Comment
Question by:dshrenik
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
7 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 35006673
I would doubt they were any different. In theory both languages should use the best possible complexity
0
 
LVL 53

Accepted Solution

by:
Infinity08 earned 1336 total points
ID: 35006744
std::map in C++ is NOT a hash table. Most implementations use a BST (binary search tree) to implement std::map, so its time complexity is quite different from that of a hash table.

For example : std::map has O(log n) search complexity for example, while a well-implemented hash table would have O(1) complexity for the same operation.
0
 

Author Comment

by:dshrenik
ID: 35006818
I'm sorry.

Can you tell if C++'s hash_map and Java's HashMap have the same time and space complexity?
0
Get 15 Days FREE Full-Featured Trial

Benefit from a mission critical IT monitoring with Monitis Premium or get it FREE for your entry level monitoring needs.
-Over 200,000 users
-More than 300,000 websites monitored
-Used in 197 countries
-Recommended by 98% of users

 
LVL 53

Expert Comment

by:Infinity08
ID: 35006854
>> Can you tell if C++'s hash_map and Java's HashMap have the same time and space complexity?

I'm not 100% sure about the Java HashMap implementation, but afaik there is a normal hash table behind it.
The std::hash_map in C++ is currently an extension, so the specific implementation depends on the implementer (but the general consensus seems to be a normal hash table).

So, yes : the complexities would be very similar, if not the same.

As always with hash tables though : a lot depends on your choice of hash function, and a proper dimensioning of the hash table (as well as collision strategy if appropriate).
0
 
LVL 35

Expert Comment

by:sarabande
ID: 35008655
can you tell about your keys? and the number of entries now and in future? is your main concern a fast read and find of existing keys or a fast insert/update/delete ?

you may think of making test implementations for either map. if you can serve realistic test data you reliably will know what is the best container for your purpose.

Sara
0
 
LVL 28

Assisted Solution

by:dpearson
dpearson earned 664 total points
ID: 35009443

Can you tell if C++'s hash_map and Java's HashMap have the same time and space complexity?

In terms of space, both will be O(n) - there is one entry in the map for each key and then a list of entries where the keys collide, but each (key,value) pair in the map will appear only once in the data structure so they're O(n) for space.

In terms of time complexity, inserts will be O(1) [locating the hashed entry is a constant time operation and adding to the end of the list of items for a key should also be a constant time operation].  Reads will be O(log n) because the process is locate the hashed entry (which is constant time) and then walk the list of items with the same hash value - which will tend to log n for a large n and a fixed map size.  (If you make your map as large as your key space then this will instead be O(1) - but that's not a typical usage pattern for maps).

C++ and Java will both have the same complexity.

Doug
0
 
LVL 53

Assisted Solution

by:Infinity08
Infinity08 earned 1336 total points
ID: 35009478
>> (If you make your map as large as your key space then this will instead be O(1) - but that's not a typical usage pattern for maps).

It is typical for many hash table needs to avoid collisions as much as possible though.
0

Featured Post

Optimize your web performance

What's in the eBook?
- Full list of reasons for poor performance
- Ultimate measures to speed things up
- Primary web monitoring types
- KPIs you should be monitoring in order to increase your ROI

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
In this post we will learn how to connect and configure Android Device (Smartphone etc.) with Android Studio. After that we will run a simple Hello World Program.
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
Suggested Courses
Course of the Month13 days, 5 hours left to enroll

777 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question