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Java Sorting

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Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Methods in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

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Java Exceptions

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Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

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Java Serialization Java transient

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Java AWT

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Swing in Java

Java Collections

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Java Generics

Generics in Java

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Annotations in Java

Java JDBC

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How to

How to convert String to String array in Java How to find length of integer in Java How to get Day Name from Date in Java How to open the Java control panel How to resolve Illegal state exceptions in Java How to reverse a linked list in java How to encrypt password in Java How to calculate time complexity of any program in Java How to check version of java in Linux How to enable java in chrome How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to add double quotes in a string in Java How to convert list to String in Java How to call a method in Java How to Set Environment Variables for Java How to sort an array in Java How to Create Immutable Classes in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to Create Singleton Class in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to find the length of an Array in Java How to Read Java JSON file How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to import packages in Java How to run applet Program in Java How to take Array Input in Java How to achieve abstraction in Java How to call static method in Java How to compare characters in Java How to compare dates in Java How to create a linked list in Java How to download Eclipse for Java How to get ASCII value of char in Java How to get the current date and time in Java How to handle NullPointerException in Java How to initialize string array in Java How to Install Java on MAC How to run java program in ubuntu How to find characters with the maximum number of times in a string java How to Set Java_home in Linux How to Split the String in Java with Delimiter How to take Multiple String Input in Java using Scanner class How to uninstall the Java in Ubuntu How to Update Java How to add Elements in Array in Java How to avoid deadlock in java How to Split String by Comma in Java How to remove special characters from String in Java How to remove last character from String in Java How to Read XML Files in Java How to download and install Eclipse in Windows How to Create an API in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Type Annotations in Java Java Stringjoiner Class Parallel Arrays Sort in Java Bifunction in java 8 Java 8 filters list Java 8 Consumer Interface in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java 12

What’s new in Java 12

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New Features of Java 14

Java 15

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Java 16

Java 16

Java 17

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Java Servlet Tutorial

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Java JSP Tutorial

Java JSP Tutorial

Hiberate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial Jenkins java net socket connection time out

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.fma() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Misc

List all files in a Directory in Java Nonagonal number in Java Null Pointer Exception in Java Package naming convention in Java Packages Program in java Pangram Program in Java PriorityBlockingQueue Class in Java Race Condition in Java Repdigit Numbers in Java Reserved Keywords in Java Rotate matrix by 90 degrees in Java Segment Tree in Java Sierpinski Number in Java Sort Dates in Java Thread Safety and How to Achieve it in Java Normal and Trace of a Matrix in Java Transient variable in Java Tribonacci series in Java Web Crawler in Java Zigzag Traversal of Binary Tree in Java Java Full Stack Java IO filenotfoundexception Java Output Formatting Java Plot Java Pop Java program to print matrix in Z form Java Set to List Java Switch string Java Thread Lifecycle: States and Stages Java Viva Questions and Answers Lazy Propagation in Segment Tree in Java Level order Traversal of a Binary Tree in Java Method chaining in Java Narcissistic Number in Java Java Case Keyword Java Try-Catch Block Java Class KeywordJava concurrency interview questions Java Continue Keyword Java CountDownLatch Java Default Keyword Java Double Keyword Java Editors Java Else Keyword Java Enum Keyword Java Extends keywordJava Finally Keyword Java Font Example of Static import in Java How Many Ways to Create Objects in Java Implementing Queue Using Array in Java Instanceof operator in Java Interchange Diagonal elements in Java Java Arrays Fill Java Char Keyword Convert list to array Java Convert milliseconds to date in Java Copy data/content from one file to another in java CRC Program in Java Creating a Jar file in Java Crown Pattern in Java Difference Between Access Specifiers and Modifiers in Java Difference Between Java and PHP Difference Between replace() and replaceall() in Java Duodecimal in Java Finding middle node of a linked list in Java Group by in Java 8 Hollow Diamond Pattern in Java How annotations work in Java Java Boyer Moore Catalan number in Java Cosmic Superclass in Java Difference between this and super in Java Fall through in Java Figurate Number in Java Java Anon Proxy Java RMI Lazy loading in Java Magnanimous Number in java Shallow copy in Java String to JSON in Java Tetranacci Number in Java Vigesimal in Java Why main method is static in Java Add Time in Java Bellman Ford Algorithm in Java Best Java Libraries Blockchain in Java Blocking Queue in Java Example Bully Algorithm code in Java Contextual keywords in Java Convert JSON File to String in Java Determine the Upper Bound of a Two-Dimensional Array in Java Java.net.ConnectionException Java.net.SocketException Web Service Response Time Calculation in Java Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Replace character in string Java String Coding Interview Questions in Java What is String in Java? 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Java Boyer Moore

A string searching or matching technique called the Boyer-Moore algorithm was created in 1977 by Robert S. Boyer and J. Strother Moore. It is the most popular and effective string-matching algorithm. Compared to the brute-force algorithm, it is substantially faster. The Boyer-Moore algorithm, its features, and its application in a Java program will all be covered in this article. It has a temporal complexity of O(nm+s). In most applications, the Boyer-Moore algorithm is the most efficient string-matching algorithm. In text editors, the «search» and «substitute» commands frequently use a simplified version of the algorithm or the entire algorithm.

Worst-case scenario

T=ssssssss……sssssss………ssssssss

P=psssssssss

The above sequence can be found in images and DNA sequences.

Characteristics of the Boyer Moore Algorithm

  • From right to left, it compares each character;
  • O(m+) time and space complexity characterize the pre-processing stage.
  • The searching step has an O(mn) complexity.
  • In the worst scenario, it compares 3n text characters when looking for a non-periodic pattern.
  • The complexity with the best performance is O(n/m).

The algorithm is based on the two heuristics listed below:

  • Character-Jump Heuristics
  • Looking-Glass Heuristics

Let's examine how the Boyer-Moore algorithm works.

The Boyer-Moore algorithm's operation

The method begins tracing characters from the pattern's rightmost character and advances leftward. It employs two pre-computed functions that shift the characters to the right and left, respectively, in the event of any mismatch and complete pattern matching. The good-suffix shift (also known as the matching shift) and the bad-character shift (or occurrence shift) are the names of these two pre-computed shift functions.

Note: Characters should be compared in a right-to-left sequence and aligned left to right to match the pattern.

Bad Character Shift

Skip alignment when there is a mismatch up until one of the following situations does not exist:

  1. Mismatch turns into a match
  2. P avoids mismatching characters

Take the text (T) and pattern (P) shown below as examples.

Boyer Moore Java

Start comparing the pattern now.

Step 1: First, align characters from left to right and compare them from right to left.

We can see that the last three characters of P correspond to those in T. T, the fourth character, is mismatched. As per the above guideline, skip alignment until a mismatch becomes a match. The seventh character (C) in P matched with C in T.

Boyer Moore Java

The above-displayed image shows the partial match.

Step 2: Move three characters to the right to match the pattern.

Compare the characters once more, this time from right to left, after moving. It matches the first character. We see that the character A is absent from the position to the left of P. P then shifts to the past mismatch character (A) in T in this instance.

Boyer Moore Java

The above-displayed image shows the procedure through which P and T attain matches.

Step 3: If P is moved past the mismatched character, we get,

Boyer Moore Java

From the above-displayed image, the pattern is matched. The sequence “CCTTTTGC” matches in both the T and P.

Note: The bad-character shift may not be good. Given that the Boyer-Moore method applies the maximum (skip characters) between the good-suffix shift and bad-character shift, it is appropriate to shift characters in this manner.

Good-Suffix Shift

Let's say that an inner loop matches the substring t. If so, skip characters up until:

  1. No mismatches exist between P and t.
  2. P moves past t.

Consider the following pattern as an example.

Boyer Moore Java

Step 1: Go from right to left and compare the characters. We can see that the last three characters of P correspond to characters in T denoted by t.

Boyer Moore Java

The above-displayed image shows the partial match.

Step 2: Continue until there is no match between P and t. The first four characters (from left to right) of P (C T T A C) correspond to the last five characters in t.

Boyer Moore Java

The above-displayed image shows the procedure through which P and t attain no matches.

Step 3: To get the match, skip three alignments. As a result, we get the match.

Boyer Moore Java

The above-displayed image shows the match. The sequence “CTTACTTAC” matches in both the T and P.

The two-shift functions described above can be defined as follows:

The good-suffix shift function is stored in a table of size m+1 called “bmGs”. The table “bmGs” is computed using a table “suff” defined as follows:

for 1 ? i < m, suff[i]=max{k : x[i-k+1 .. i]=x[m-k .. m-1]} 

The bad-character shift function is stored in a table bmBc of size s. For c in ∑:

bmBc[c] = min{i : 1 ? i <m-1 and x[m-1-i]=c} if c occurs in x, m otherwise. 

Pattern Matching Example Using Boyer Moore

Think about the following pattern.

Boyer Moore Java

Let's begin matching.

Step 1: Characters should be compared from right to left. The first character is mismatched, as G does not match with T.

Boyer Moore Java

Step 2: Skip the following few characters until we find a match. After six characters, a match is made. The good suffix shift rule will not be applicable in this case.

Boyer Moore Java

P moves past mismatch character (i.e. G), according to bad character shift.

Boyer Moore Java

Step 3: Compare characters once more from right to left. We can observe that P's first three characters match (t) with T, but its fourth character does not.

Boyer Moore Java

Both the bad and good character suffix can be used in this situation. When the bad character suffix is used, only one character is skipped. The good character suffix ignores two alignments when used. Therefore, since the algorithm says to skip additional alignments, we will use the good character suffix. Consequently, we omit two alignments.

Boyer Moore Java

Three characters of alignment are changed, and the result is:

Boyer Moore Java

Here, we can see that C is missing from P's area to the left. Good character alignments skip seven alignments, while bad character alignments skip two alignments.

Step 4: We can observe that the string is matched after changing a few characters.

Boyer Moore Java

We skipped 15 alignments in the earlier pattern, and 11 T characters were ignored.

Boyer Moore Pre-processing Phases

The following definition applies to calculated skips for the patterns T: A A T C A A T A G C and P: T C G C. The bad character shift function was employed in the above pattern.

Boyer Moore Java

The above table (characters) shows the number of skip alignments.

Pseudo Code for the Boyer Moore Algorithm

BoyerMooreMatch(H, T, ?)  
K<- lastOccurenceFunction(T, ?)  
i <- m-1  
j <- m-1  
repeat  
                    if H[i]=T[j]  
                             if j=0  
                                  return i {match at i}  
                             else  
                                  i <- i-1  
                                  j <- j-1  
                    else  
                         {character-jump}  
                         K<-K[H[i]]  
                         i <- i +m -min(j, 1+ l)  
                         j <- m-1  
until i>n-1  
return-1 {no match}  

Java Program for Pattern Searching

Let's look at the pattern-finding Java program. The brute-force string searching algorithm is implemented in the following program.

File name: PatternSearchingExample.java

import java.util.HashMap;  
import java.util.Map;  
public class PatternSearchingExample  
{  
/**  
* @example text -- trace the text to see if it contains pattern 
* @example pattern -- look for this text inside the text parameter 
* @return -- return index of the first match or -1 if not found 
*/  
public static int findBruteForce(char[] text, char[] pattern)   
{  
System.out.println("Brute force looking for " + String.valueOf(pattern) + " in " + String.valueOf(text)) ;  
int n = text.length ;  
int m = pattern.length ;  
//checks if the string is empty  
if (m == 0) return 0 ;  
//brute force it -- loop over all characters in text O(n)  
for (int i=0;i<=n-m;i++)   
{ //index into the text  
//loop over all characters in pattern while characters match O(m)  
//index into the pattern  
int k = 0 ;   
while (k<m && text[i+k] == pattern[k])   
{  
k++ ;  
}  
//if at the end of the pattern, then found match starting at index i in text  
if (k==m)   
{  
System.out.println("\tFound match in the given text at index " + i) ;  
return i ;  
}  
}  
//if a match is not found  
System.out.println("\tNo match found in the given text.") ;  
return -1 ;  
}  
/** 
 
* @example text -- search this text to see if it contains pattern 
* @example pattern -- look for this text inside the text parameter 
* @return -- return index of the first match or -1 if not found 
*/  
public static int findBoyerMoore(char[] text, char[] pattern)   
{  
System.out.println("Boyer-Moore looking for " + String.valueOf(pattern) + " in " + String.valueOf(text)) ;  //valueOf method is used
int n = text.length ;  // n stores length of the text
int m = pattern.length ;  
// Test for empty string  
if (m == 0) return 0 ;  
// Initialization, create Map of last position of each character = O(n)  
Map<Character, Integer> last = new HashMap<>() ;  //Map
for (int i = 0; i < n; i++)   
{  
// set all chars, by default, to -1      
last.put(text[i], -1) ;     
}          
for (int i = 0; i < m; i++)   
{  
// update last seen positions      
last.put(pattern[i], i) ;   
}  
//Start with the end of the pattern aligned at index m-1 in the text.   
//index into the text  
int i = m - 1 ;    
// index into the pattern  
int k = m - 1 ;    
while (i < n)   
{   
if (text[i] == pattern[k])   
{  
// match! return i if complete match; otherwise, keep checking      
if (k == 0)   
{  
System.out.println("\tFound match in the given text at index " + i) ;  
return i ;   
}  
i = i - 1 ; 
k--;   
}   
else   
{ // jump step + restart at end of pattern  
//iterate over the text   
i += m - Math.min(k, 1 + last.get(text[i])) ;    
//move to the end of the pattern  
k = m - 1 ;   
}  
}  
System.out.println("\tNo match found in the given text.") ;  
// prints as not found  
return -1 ;   
}  
public static void main(String args[])   
{  
char[] text = "abcfefabddef".toCharArray() ;  //string to character array
char[] pattern = "abddef".toCharArray() ;  //string to character array
//function calling  
findBruteForce(text,pattern) ;  //calls the findBruteForce function
findBoyerMoore(text,pattern) ;          //calls the findBruteForce function
}  
}   

Output

Boyer Moore Java

The above-displayed image is the output for the above program, and The output says that "abddef” is present in the “abcfefabddef” at index 6.

Let's use a Java program to implement the algorithm.

The Boyer Moore Java Program

Let's use a Java program to implement the Boyer-Moore algorithm and search pattern.

Program 1

Filename: BoyerMooreImplementation.java

public class BoyerMooreImplementation  
{  
static int NO_OF_CHARS = 256;   
static int max (int a, int b)   
{   
return (a > b)? a: b;   
}   
static void badCharHeuristic( char []str, int size, int badchar[])   
{   
int i;   
for (i = 0; i < NO_OF_CHARS; i++)   
badchar[i] = -1;   
for (i = 0; i < size; i++)   
badchar[(int) str[i]] = i;   
}   
static void search( char txt[],  char pat[])   
{   
int m = pat.length;   
int n = txt.length;   
int badchar[] = new int[NO_OF_CHARS];   
//function calling  
badCharHeuristic(pat, m, badchar);   
int s = 0;    
while(s <= (n - m))   
{   
int j = m-1;   
while(j >= 0 && pat[j] == txt[s+j])   
j--;   
if (j < 0)   
{   
System.out.println("Patterns occur at character = " + s);   
s += (s+m < n)? m-badchar[txt[s+m]] : 1;   
}   
else  
s += max(1, j - badchar[txt[s+j]]);   
}   
}   
public static void main(String args[])   
{   
//text in which pattern occurs  
char txt[] = "123651266512".toCharArray();   
//pattern to search  
char pat[] = "12".toCharArray();   
search(txt, pat);   
}   
}  

Output

Boyer Moore Java

Let's look at another Java program where we have distinct logic for pattern finding implemented. The code that follows next determines whether the text contains the required pattern.

Program 2

Filename: BoyerMooreExample.java

public class BoyerMooreExample  
{  
public static void main(String args[])   
{  
        System.out.println("Matching Pattern");  
        test("aabbccdef", "cde", 0);  
        test("zzzzaaapppxyzabc", "pqrs", 1);  
        test("mango", "ngo", 2);  
        test("abc", "d", -1);  
        test("catdog", "tdo", 2);  
        test("pqrsabcdxyzamnop", "cdxyza", 1);  
        test("cool", "", 0);  
        test("", "car", -1);  
}  
    public static void test(String text, String word, int exp)   
    {  
        char[] textC = text.toCharArray();  
        char[] wordC = word.toCharArray();  
        int result = bm(textC, wordC);  
        if(result == exp)  
            System.out.println("Pattern Matched");  
        else   
        {  
            System.out.println("Pattern Not Matched");  
            System.out.println("\ttext: " + text);  
            System.out.println("\tword: " + word);  
            System.out.println("\texp: " + exp + ", res: " + result);  
        }//end of else  
    }//end of function  
    public static int[] makeD1(char[] pat)   
    {  
        int[] table = new int[255];  
        for(int i=0; i<255; i++)  
            table[i] = pat.length;  
        for(int i=0; i<pat.length-1; i++)  
            table[pat[i]] = pat.length-1-i;  
        return table;  
    }//end of the function  
    public static boolean isPrefix(char[] word, int pos)   
    {  
        int suffixlen = word.length - pos;  
        for(int i=0; i<suffixlen; i++)  
            if(word[i] != word[pos+i])  
                return false;  
        return true;  
    }//end of the function  
    public static int suffix_length(char[] word, int pos)   
    {  
        int i;  
        for(i=0; ((word[pos-i] == word[word.length-1-i]) & (i < pos)); i++)  
            {  
                  
            }//end of for loop  
        return i;  
    }//end of the function   
    public static int[] makeD2(char[] pat)   
    {  
        int[] delta2 = new int[pat.length];  
        int p;  
        int last_prefix_index = pat.length - 1;  
        for(p = pat.length-1; p>=0; p--)   
        {  
            if(isPrefix(pat, p+1))  
                last_prefix_index = p+1;  
            delta2[p] = last_prefix_index + (pat.length-1-p);  
        }//end of for loop  
        for(p=0; p<pat.length-1; p++)   
        {  
            int slen = suffix_length(pat, p);  
            if(pat[p-slen] != pat[pat.length-1-slen])  
                delta2[pat.length-1-slen] = pat.length-1-p+slen;  
        }//end of for loop  
        return delta2;  
    }//end of function  
    public static int bm(char[] string, char[] pat)   
    {  
        int[] d1 = makeD1(pat);  
        int[] d2 = makeD2(pat);  
        int i = pat.length-1;  
        while(i < string.length)   
        {  
            int j = pat.length-1;  
            while(j>=0 && (string[i] == pat[j]))   
            {  
                i--; //decrement i by 1  
                j--; //decrement j by 1  
            }//end of while  
            if(j < 0)  
                return (i+1);  
            i += Math.max(d1[string[i]], d2[j]);  
        } //end of while  
        return -1;  
    }//end of the function  
}  

Output

Boyer Moore Java



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