Java: Given a String find the distinct characters in it and count it

 

Given a String find the distinct characters in it and count it.

 

Input:  DISTINCT

Output: DSNC 4

Approach:

·         Well, to approach this problem there are ‘N’ number of ways.

·         Convert string to character array.

·         Use HashMap to hold keys as characters and count as values.

·         Use any Set implemented Class add the characters and get the count. (we can get distinct but need to remove repeated character)

·         Use traditional Brute force method with multiple for loops, check each character and get the count.

·         Create your custom class with member variables as character and count add in to an ArrayList and get the count.

·         Etc.

Thought:

·         What if we are not suppose to use any additional data structures?

·         When such problems come in – the first thought will come to our mind is- let’s convert to character Array so that we can navigate it easily.

·         The focus is on only one method of String class: toCharArray()

·         But String class have provided many other methods- even if we know those we fail to identify.

·         When a problem is given to you, split the problem in to tokens (in your mind) and analyze.

·         Tokens are like:

o   String

o   Characters

o   Distinct

o   Count

·         You can get answers in the question many a times.

·         But the focus and weightage we give to specific token and revolve around it.

·         Now, can we recall any methods in String class which are helpful?

Method	Description	ReturnType
indexOf(int ch) OR indexOf(String str)	Returns the index (int value) within this string of the first occurrence of the specified character/substring.	int
lastIndexOf(int ch) OR lastIndexOf(String str)	Returns the index within this string of the last occurrence of the specified character/substring.	int
length()	Returns the length of this string.	int
charAt(int index)	Returns the char value at the specified index.	char
replace(char oldChar, char newChar)	Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.	String
replace(CharSequence target, CharSequence replacement)	Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.	String
replaceAll(String regex, String replacement)	Replaces each substring of this string that matches the given regular expression with the given replacement.	String

 

Now knowing the above methods can we try to write code for the problem?

(click on the image to expand)

Well, trying to use Java Streams to solve the same problem.

(click on the image to expand)
 

Note:

·         The above solutions are not the ultimate or the only way to approach the problem.

·         Attaching screenshot because you need to practice than copying code and executing in IDE.

·         As I said there are ‘N’ number of ways to solve the issue, here I tried using inbuilt methods from String class and get the solution.

·         Comments and suggestions are always welcome. git link: https://github.com/failed-peanut/java