In this post we’ll see a Java program to find duplicate characters in a String along with repetition count of the duplicates.
Finding duplicates characters in a String and the repetition count program is easy to write using a HashMap but you may be asked to write it without using any Java collection. In this post we’ll see both solutions.
Java program to find duplicate characters in a String
If you are not using HashMap then you can iterate the passed String in an outer and inner loop and check if the characters are equal or not. If equal, then increment the count. In case characters are equal you also need to remove that character from the String so that it is not counted again in further iterations.
public class DuplicateChars {
public static void main(String[] args) {
findDuplicateCharsWithCount("kakatua parrot is a bird");
System.out.println("------------");
findDuplicateCharsWithCount("John was jealous");
System.out.println("------------");
findDuplicateCharsWithCount("rats");
}
private static void findDuplicateCharsWithCount(String str) {
System.out.println("Duplicates in- "+ str);
int count;
for(int i = 0; i < str.length(); i++) {
count = 1;
//Take one char at a time
char c = str.charAt(i);
// don't count the spaces
if(c == '')
continue;
for(int j = i + 1; j < str.length(); j++) {
if(c == str.charAt(j)) {
count++;
// remove the char so that it is not picked again
// in another iteration
str = str.substring(0, j) + str.substring(j+ 1);
}
}
if(count > 1) {
System.out.println(c + " found " + count + " times");
}
}
}
}
Output
Duplicates in- kakatua parrot is a bird
k found 2 times
a found 5 times
t found 2 times
r found 3 times
i found 2 times
------------
Duplicates in- John was jealous
o found 2 times
a found 2 times
s found 2 times
------------
Duplicates in- rats
Java program to find duplicate characters in a String using HashMap
If you are writing a Java program to find duplicate characters in a String along with repetition count using HahsMap then you can store each char of the String as a key and starting count as 1 which becomes the value. In each iteration check if key already exists, if yes then increment the count (by accessing the value for that key).
public class DuplicateChars {
public static void main(String[] args) {
findDuplicateCharsWithCount("kakatua parrot is a bird");
System.out.println("------------");
findDuplicateCharsWithCount("John was jealous");
System.out.println("------------");
findDuplicateCharsWithCount("rats");
}
private static void findDuplicateCharsWithCount(String str) {
System.out.println("Duplicates in- "+ str);
char[] strArr = str.toCharArray();
Map<Character, Integer> countMap = new HashMap<>();
for(char c : strArr) {
// We don't need to count spaces
if(c == '')
continue;
if(countMap.containsKey(c)) {
countMap.put(c, countMap.get(c) + 1);
}else {
countMap.put(c, 1);
}
}
// Displaying the map values
Set<Map.Entry<Character, Integer>> countSet = countMap.entrySet();
for(Map.Entry<Character, Integer> entry : countSet){
if(entry.getValue() > 1) {
System.out.println(entry.getKey() + " found " + entry.getValue() + " times");
}
}
}
}
Output
Duplicates in- kakatua parrot is a bird
a found 5 times
r found 3 times
t found 2 times
i found 2 times
k found 2 times
------------
Duplicates in- John was jealous
a found 2 times
s found 2 times
o found 2 times
------------
Duplicates in- rats
That's all for this topic Find Duplicate Characters in a String With Repetition Count - Java Program. If you have any doubt or any suggestions to make please drop a comment. Thanks!
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