Java program to count the occurrence of each character in a string using Hashmap
Last Updated :
01 Dec, 2022
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Given a string, the task is to write a program in Java which prints the number of occurrences of each character in a string.
Examples:
Input: str = "GeeksForGeeks" Output: r 1 s 2 e 4 F 1 G 2 k 2 o 1 Input: str = "Ajit" Output: A 1 t 1 i 1 j 1
An approach using frequency[] array has already been discussed in the previous post. In this program an approach using Hashmap in Java has been discussed.
- Declare a Hashmap in Java of {char, int}.
- Traverse in the string, check if the Hashmap already contains the traversed character or not.
- If it is present, then increase its count using get() and put() function in Hashmap.
- Once the traversal is completed, traverse in the Hashmap and print the character and its frequency.
Below is the implementation of the above approach.
- Java
Java
// Java program to count frequencies of// characters in string using Hashmapimport java.io.*;import java.util.*;class OccurrenceOfCharInString { static void characterCount(String inputString) { // Creating a HashMap containing char // as a key and occurrences as a value HashMap<Character, Integer> charCountMap = new HashMap<Character, Integer>(); // Converting given string to char array char[] strArray = inputString.toCharArray(); // checking each char of strArray for (char c : strArray) { if (charCountMap.containsKey(c)) { // If char is present in charCountMap, // incrementing it's count by 1 charCountMap.put(c, charCountMap.get(c) + 1); } else { // If char is not present in charCountMap, // putting this char to charCountMap with 1 as it's value charCountMap.put(c, 1); } } // Printing the charCountMap for (Map.Entry entry : charCountMap.entrySet()) { System.out.println(entry.getKey() + " " + entry.getValue()); } } // Driver Code public static void main(String[] args) { String str = "Ajit"; characterCount(str); }} |
Output:
A 1 t 1 i 1 j 1
Time complexity: O(n) where n is length of given string
Auxiliary Space: O(n)
