anujparikh / strings

Strings Data Structure and Numbers

Introduction

• Strings are defined as an array of characters.
• The difference between a character array and a string is the string is terminated with a special character \0
• In java, objects of String are immutable which means a constant and cannot be changed once created

Some of constructor functions for Strings

• String(byte[] byte_arr)
• String(char[] char_arr)
• String(char[] char_array, int start_index, int count)
• String(StringBuffer s_buffer)
• String(StringBuilder s_builder)

Methods in java.util.String Class

Methods	Description	Returns	Notes
length	Returns the number of characters in the String	int
charAt(int i)	Returns the character at ith index	Char
substring(int i)	Return the substring from the ith index character to end	String
substring(int i, int j)	Returns the substring from i to j-1 index	String
concat(String str)	Concatenates specified string to the end of this string	String
indexOf(String str)	Returns the index within the string of the first occurrence of the specified string	int	If not present will return -1
indexOf(String str, int i)	Returns the index within the string of the first occurrence of the specified string, starting at the specified index	int
lastIndexOf(String str)	Returns the index within the string of the last occurrence of the specified string	int
equals(String s)	Compares this string to the specified string	boolean
equalsIgnoreCase(String s)	Compares string to another string, ignoring case considerations	boolean
toLowerCase(String s)	Converts all the characters in the String to lower case	String
toUpperCase(String s)	Converts all the characters in the String to upper case	String
trim	Returns the copy of the String, by removing whitespaces at both ends. It does not affect whitespaces in the middle	String
replace(char oldChar, char newChar)	Returns new string by replacing all occurrences of oldChar with newChar	String

• Some other methods are
  • compareTo(String s)
  • compareToIgnoreCase(String s)

Methods in java.util.Character Class

Methods	Description	Returns	Notes
isLetter(char c)	This method is used to determine whether the specified char value(ch) is a letter or not	boolean	only within [A-Za-z]
isDigit(char c)	This method is used to determine whether the specified char value(ch) is a digit or not	boolean
isWhitespace(char c)	It determines whether the specified char value(ch) is white space	boolean

• Some other methods are
  • isUpperCase(char c)
  • toUpperCase(char c)
  • isLowerCase(char c)
  • toLowerCase(char c)

Common syntax

• Creating a String

String s = “Random String”;
String s = new String (“Random String”);

• Replace non-alphanumeric characters within String

s.replaceAll("[^A-Za-z0-9]", "");

Examples

• Reverse String: Solution (Easy)
• Reverse Integer: Solution (Easy)
• Palindrome Number Solution (Easy)
• Roman To Integer Solution (Easy)
• First Unique Character: Solution (Easy)
• Valid Anagram: Solution (Easy)
• Valid Palindrome: Solution (Easy)
• String to Integer (atoi): Solution (Easy)
• Implement strStr(): Solution (Easy)
• Count And Say: Solution (Easy)
• Longest Common Prefix: Solution (Easy)
• Longest Substring Without Repeating Characters Solution (Medium)
• Longest Palindromic Substring Solution (Medium) - This can also be done with Dynamic Programming
• ZigZag Conversion Solution (Medium)
• Valid Parentheses Solution (Easy)