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ACM Training Session

BRAC UNIVERSITY

3/8/2012

Raduan & Mahbub

This work is licensed under a Creative Commons Attribution-NonCommercial-

ShareAlike 3.0 Unported License.

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Raduanul Islam (10101024) & S. Mahbub – Uz – Zaman (09301004)

String (Java)

Frequently Asked Questions (FAQ)

1. What is String?

A string is a sequence of characters treated as a single unit. A string may include letters,

digits and various special characters, such as +, -, *, / and $. A string is an object of

class String. [For more info read Chapter 29 of Java How to Program]

2. Is String a primitive data type in Java?

No String is not a primitive data type in Java, even though it is one of the most

extensively used object. Strings in Java are instances of String class.

[http://docs.oracle.com/javase/tutorial/java/data/strings.html]

3. Is the + operator overloaded?

Java does not have operator overloading, but string concatenation is a special case. When

the + operator is applied to a String, the two values are appended as a new String. If you

use the + operator with a String and a primitive value, such as an int or long, the Java

interpreter implicitly converts the primitive value a string representation and concatenates

them.

4. How can you say the + operator is not overloaded in Java!

The plus operator for Java strings is a limited exceptional case that is practically the same

as operator overloading. It’s a fine distinction but using + to append object contents is not

a general case in Java, it only applies to String objects. An equivalent append operation

may be meaningful and useful for data storage types but does not have a general

application and is not implemented in Java.

// Compiler error: "operator + cannot be applied to java.util.Vector"

// Vector vector = new Vector() + new Vector();

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Classes that you will need for ACM

1. String (http://docs.oracle.com/javase/6/docs/api/java/lang/String.html)

2. StringTokenizer (http://docs.oracle.com/javase/6/docs/api/java/util/StringTokenizer.html)

3. StringBuffer (docs.oracle.com/javase/6/docs/api/java/lang/StringBuffer.html)

4. Character (docs.oracle.com/javase/6/docs/api/java/lang/Character.html)

5. Matcher (http://docs.oracle.com/javase/6/docs/api/java/util/regex/Matcher.html)

6. Pattern (http://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html)

// you have to learn some basic methods provided by these classes like

trim(), length(), toUpperCase() etc

The following topics will be needed for ACM

1. String Matching (Knuth Morris Pratt (KMP), Rabin – Karp, Aho – Corasick, Boyer –

Moore, Suffix Tree/Trie/Array, Finite State Automata)

2. Regular Expressions

3. String Permutation (SEPA)

4. Determine Subsequence

5. Determine Anagram

6. Determine Palindrome (check palindrome or make palindrome [DP])

7. Longest common Subsequence (DP)

8. Longest common Substring and Longest repeated Substring

9. Longest common prefix

10. Shortest common Superstring

11. String Alignment (Edit/Levenshetin Distance) (DP)

12. Hashing

13. Burrows wheeler transform

14. Radix Tree

15. Suffix automaton

http://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html

http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#toUpperCase%28%29

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Some Common Definitions

1. Anagram: A word or phrase formed by reordering the letters of another word or phrase,

such as satin to stain.

2. Permutation: You are given two strings A and B. B will be said the permutation of A, if

you can make B from A by re-arranging some (or none) characters.

aabc is a permutation of caba

3. Substring: A substring (or factor) of a string T = t1…..tn is a string ̂ = t1+i…..tm+i , where

0 i and m + i n . A substring of a string is a prefix of a suffix of the string, and

equivalently a suffix of a prefix. If ̂ is a substring of T, it is also a subsequence, which is

a more general concept.

Given a pattern P, you can find its occurrences in a string T with a string searching

algorithm.

Finding the longest string which is equal to a substring of two or more strings is known

as the longest common substring problem.

Example: The string ana is equal to substrings (and subsequences) of banana at two

different offsets:

banana

|||||

ana||

|||

ana

Substrings are also called subwords (in America) or factors (in Europe). It is also a

subsequence

4. Subsequence: You are given two strings A and B. B will be said the subsequence of A, if

you can make B from A by deleting some (or none) characters. For example, ABD is a

subsequence of ABCDEF. Where, order of the elements is preserved.

5. Prefix: A prefix of a string T = t1…..tn is a string ̂ = t1…..tm, where m n. A

proper prefix of a string is not equal to the string itself (0 ); some sources

in

addition restrict a proper prefix to be non-empty (0 < m < n). A prefix can be seen as

a special case of a substring.

Example: The string ban is equal to a prefix (and substring and subsequence) of the string

banana:

banana

|||

Ban

A B C D E F

A B C D E F

http://en.wikipedia.org/wiki/Subsequence

http://en.wikipedia.org/wiki/String_searching_algorithm

http://en.wikipedia.org/wiki/String_searching_algorithm

http://en.wikipedia.org/wiki/Longest_common_substring_problem

http://en.wikipedia.org/wiki/Subsequence

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6. Suffix: A suffix of a string T = t1…..tn is a string ̂ = tn – m + 1…..tm where m n. A

proper suffix of a string is not equal to the string itself (0 ); again, a more

restricted interpretation is that it is also not empty (0 < m < n). A suffix can be seen as a

special case of a substring.

Example: The string nana is equal to a suffix (and substring and subsequence) of the

string banana:

banana

||||

nana

7. Border:

A border is suffix and prefix of the same string, e.g. "bab" is a border of "babab".

Different Characters:

Uppercase Letters: A, B, C, D, E

Lowercase Letters: a, b, c, d, e

Digits: 0, 1, 2, 3, 4

Punctuation: comma (,), full stop/period (.)

Control/non-printing/escape characters: carriage return, tab, newline

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Sample I/O

// Test Case Style

2

Runway

Tintin

// EOF Style

CSE

ECE

EEE

null (End Of File)

// Blank Line Style

Apple

Microsoft

Yahoo

(Blank Line)

// Reading A String after Reading an Integer Problem

1

Ki holo

/* nextInt() does not change the line so after reading 1; when we hit enter

causes the endOfLine (\r\n). This EOL is read by nextLine() and that’s why

“Ki holo” never read by nextLine() */

[http://docs.oracle.com/javase/6/docs/api/java/util/Scanner.html]

// Sentinel Style

Mili

Micro

Nano

Stop (Sentinel)

// Mixed

3

X 2

Y 3

Z 5

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Important Links

1. http://www.leepoint.net/notes-java/data/expressions/22compareobjects.html

Resources:

1. http://en.wikipedia.org/wiki/Wiki

2. http://www.codestyle.org

3. http://www.thefreedictionary.com

http://www.leepoint.net/notes-java/data/expressions/22compareobjects.html

http://www.codestyle.org/

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