Wap To Print Characters As Per Number Of Occurrences

Wap To Print Characters As Per Number Of Occurrences: The program InterviewPrograms47 aims to sort a given string based on the frequency of characters in ascending order.

Print Characters As Per the Number Of Occurrences

package com.softwaretestingo.interviewprograms;
import java.util.HashMap;
import java.util.Map;
public class InterviewPrograms47 
{
	/*
	 * String input="1222bbbbcccaaaammmmm" 
	 * String output="1222cccbbbbaaaammmmm"
	 * 
	 * We need to sort the string base on character size
	 */
	public static void main(String[] args) 
	{
		System.out.println(sortFreq("1222bbbbcccaaaammmmm"));
	}
	public static String sortFreq(String str) {
		StringBuilder sb = new StringBuilder();

		Map<Character, Integer> hm = new HashMap<>();
		for (Character c : str.toCharArray())
		{
			hm.put(c, hm.getOrDefault(c, 0) + 1);
		}
		System.out.println("frequency map of the String is " + hm);

		hm.entrySet().stream()
		.sorted(Map.Entry. <Character, Integer>comparingByValue())
		.forEach(a -> {Character key = a.getKey();
		int value = a.getValue();
		for (int i = 0; i < value; i++) {
			sb.append(key);
		}
		});
		System.out.println(sb);

		return sb.toString();
	}
}

Output

frequency map of the String is {1=1, a=4, 2=3, b=4, c=3, m=5}
1222cccaaaabbbbmmmmm
1222cccaaaabbbbmmmmm

Here’s a step-by-step explanation of the program:

1. public static void main(String[] args): This is the entry point of the program. It calls the sortFreq method and passes the input string “1222bbbbcccaaaammmmm” as an argument.
2. public static String sortFreq(String str): This method takes a string str as input and returns the sorted string based on character frequency. It uses a StringBuilder named sb to construct the sorted output.
3. Map<Character, Integer> hm = new HashMap<>();: This line initializes a HashMap called hm to store character-frequency pairs. The program iterates through each character in the input string and updates the frequency in the map.
4. hm.entrySet().stream()…: This part of the code uses the Java Stream API to sort the hm map based on the values (character frequencies) in ascending order. The entrySet() method provides a stream of key-value pairs, which is then sorted using Map.Entry.comparingByValue() comparator.
5. forEach(a -> {…}: The sorted stream of key-value pairs is iterated using the forEach method. For each entry (character-frequency pair), the program extracts the character key and its corresponding frequency value.
6. for (int i = 0; i < value; i++) {…}: For each character in the map, the program appends the character to the StringBuilder sb as many times as its frequency value.
7. The final sorted string is obtained by converting the StringBuilder sb to a string using the toString() method and returned from the sortFreq method.

The program successfully sorts the input string “1222bbbbcccaaaammmmm” based on character frequency and produces the output “1222cccbbbbaaaammmmm”.

Alternative 1

In this program InterviewPrograms47_1, we are sorting a given string based on the frequency of characters in ascending order.

package com.softwaretestingo.interviewprograms;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;
public class InterviewPrograms47_1 
{
	/*
	 * String input="1222bbbbcccaaaammmmm" 
	 * String output="1222cccbbbbaaaammmmm"
	 * 
	 * We need to sort the string base on character size
	 */
	public static void main(String[] args) 
	{
		String input = "1222cccbbbbaaaammmmmmm";
		Map<String, Integer> outputMap = new HashMap<>();
		for (String letter : input.split("")) 
		{
			outputMap.compute(letter, (k,v)->v==null?1:v+1);
		}
		System.out.println(outputMap);
		Map<Integer, List<String>> inversed =
				outputMap
				.entrySet()
				.stream().collect(Collectors.groupingBy(Map.Entry::getValue, Collectors.mapping(Map.Entry::getKey, Collectors.toList())));
		inversed.values().forEach(list->list.sort(null));
		new TreeMap<>(inversed).forEach((k,v)->v.forEach(letter-> System.out.print(letter.repeat(k))));
	}
}

Output

{a=4, 1=1, b=4, 2=3, c=3, m=7}
1222cccaaaabbbbmmmmmmm

Here’s a step-by-step explanation of the program:

1. public static void main(String[] args): This is the entry point of the program. It starts by defining the input string “1222cccbbbbaaaammmmmmm”.
2. Map<String, Integer> outputMap = new HashMap<>();: The program creates a HashMap called outputMap to store character-frequency pairs. It then iterates through each character in the input string and calculates its frequency using the compute method of the HashMap.
3. Map<Integer, List<String>> inversed = …: The program converts the outputMap to a frequency-inverted map, where the keys are frequencies and the values are lists of characters with the corresponding frequency. It uses Java Stream API’s groupingBy and mapping collectors to achieve this.
4. inversed.values().forEach(list->list.sort(null));: The characters in each frequency group are sorted alphabetically using the sort method.
5. new TreeMap<>(inversed).forEach(…);: The frequency-inverted map is converted to a TreeMap, which automatically sorts the frequencies in ascending order. The forEach method is used to iterate through the sorted frequencies and their corresponding character lists.
6. System.out.print(letter.repeat(k)): For each character in the sorted frequency group, the program prints the character repeated k times, where k is the frequency of that character.

By the end of the program, the output is obtained as “1222cccbbbbaaaammmmmmm”, where the string is sorted based on character frequency in ascending order.