How To Count Occurrences Of A Grapheme Inwards String - Coffee Programming Practise Example

Write a plan to count the set out of occurrences of a grapheme inwards String is i of the mutual programming interview questions non simply inwards Java but too inwards other programming languages similar C or C++.  As String inwards a real pop theme on programming interviews together with in that place are lot of expert programming do on String similar "count set out of vowels or consonants inwards String", "count set out of characters inwards String" , How to opposite String inwards Java using recursion or without using StringBuffer etc, it becomes extremely of import to conduct maintain corporation cognition of String in Java or whatever other programming language. Though, this inquiry is to a greater extent than ofttimes than non used to exam candidate's coding mightiness i.e. whether he tin convert logic to code or not.

In Interview, close of the fourth dimension Interviewer volition inquire you lot to write a plan without using whatever API method,  as Java is real rich together with it e'er around variety of dainty method to produce the job, But it too of import to know rich Java together with opened upward origin libraries for writing production lineament code.

Anyway, inwards this question, nosotros volition run across both API based together with non-API based(except few) ways to count a set out of occurrences of a grapheme inwards String on Java.

Java plan to count occurrences of a grapheme inwards String

static method countOccurrenceOf(String, character) which takes a String together with grapheme together with returns occurrence of grapheme into that String.

After that, nosotros volition run across Apache park StringUtils course of didactics for counting occurrence of a grapheme inwards String. Apache park StringUtils render countMatches() method which tin hold upward used to count the occurrence of i grapheme or substring.

Finally, nosotros volition run across the close uncomplicated agency of counting grapheme using measure for loop together with Java v enhanced for loop. This solution tin hold upward extended non simply to finding the occurrence of grapheme but too finding occurrences of a substring.

Btw, if you lot are solving this inquiry every bit component division of your Java interview preparation, you lot tin too cheque Cracking the Coding Interview, a collection of 189 programming questions together with solutions from diverse programming labor interviews. Your perfect companion for developing coding feel required solving these kinds of problems on interviews. 

Now, let's run across the Java plan to count set out of occurrence of whatever grapheme on String:

import org.springframework.util.StringUtils;

/**
 * Java plan to count the set out of occurrence of whatever grapheme on String.
 * @author Javin Paul
 */
public class CountCharacters {

    public static void main(String args[]) {
         
        String input = "Today is Monday"; //count set out of "a" on this String.
     
        //Using Spring framework StringUtils course of didactics for finding occurrence of around other String
        int count = StringUtils.countOccurrencesOf(input, "a");
     
        System.out.println("count of occurrence of grapheme 'a' on String: " +

                " Today is Monday' using Spring StringUtils " + count);

     
        //Using Apache park lang StringUtils class
        int set out = org.apache.commons.lang.StringUtils.countMatches(input, "a");
        System.out.println("count of grapheme 'a' on String: 'Today is Monday' using park StringUtils " + number);
     
        //counting occurrence of grapheme amongst loop
        int charCount = 0;
        for(int i =0 ; i<input.length(); i++){
            if(input.charAt(i) == 'a'){
                charCount++;
            }
        }
        System.out.println("count of grapheme 'a' on String: 'Today is Monday' using for loop  " + charCount);
     
        //a to a greater extent than elegant agency of counting occurrence of grapheme inwards String using foreach loop
     
        charCount = 0; //resetting grapheme count
        for(char ch: input.toCharArray()){
            if(ch == 'a'){
                charCount++;
            }
        }    
        System.out.println("count of grapheme 'a' on String: 'Today is Monday' using for each loop  " + charCount);
    }
 
       
}

Output
count of occurrence of grapheme 'a' on String: 'Today is Monday' using Spring StringUtils 2
count of grapheme 'a' on String: 'Today is Monday' using park StringUtils 2
count of grapheme 'a' on String: 'Today is Monday' using for loop  2
count of grapheme 'a' on String: 'Today is Monday' using for each loop  2

Well, the beauty of this questions is that Interviewer tin twist it on many ways, they tin inquire you lot to write a recursive component division to count occurrences of a detail character or they tin fifty-fifty inquire to count how many times each grapheme has appeared.

So if a String contains multiple characters together with you lot demand to shop count of each character, regard using HashMap for storing grapheme every bit fundamental together with set out of occurrence every bit value. Though in that place are other ways of doing it every bit good but I similar the HashMap agency of counting grapheme for simplicity.

Further Learning
The Coding Interview Bootcamp: Algorithms + Data Structures
Data Structures together with Algorithms: Deep Dive Using Java
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