Run Length Encoding and Decoding (original) (raw)

Last Updated : 9 May, 2026

Given a string **s, implement a function encode that performs run-length encoding on the string. Run-length encoding is a form of compression where consecutive occurrences of the same character are replaced by the character followed by the count of its occurrences.

**Input: s = aaaabbbccc
**Output: a4b3c3
**Explanation: The character 'a' repeated 4 times consecutively and 'b' 3 times, 'c' also 3 times, so answer for this test case is a4b3c3.

**Input: s = abbbcdddd
**Output: a1b3c1d4
**Explanation: The character 'a' is repeated 1 time, 'b' 3 times, 'c' 1 time and 'd' repeated 4 times, so answer for this test case is a1b3c1d4.

Try It Yourself

Using Iteration (Run-Length Encoding) - O(n) Time and O(n) Space

Follow the steps below to solve this problem:

1. Pick the first character from the source string.
2. Append the picked character to the destination string.
3. Count the number of subsequent occurrences of the picked character and append the count to the destination string.
4. Pick the next character and repeat steps 2, 3 and 4 if the end of the string is NOT reached.

Below is the implementation of the above approach:

C++ `

#include #include using namespace std;

// Function to implement run length encoding string encode(string &s) { string result = ""; int n = s.length();

for (int i = 0; i < n; i++) {

    // Count occurrences of current character
    int count = 1;
    while (i < n - 1 && s[i] == s[i + 1]) {
        count++;
        i++;
    }

    // Append character and its count to result
    result += s[i];
    result += to_string(count);
}

return result;

}

// Driver code int main() { string str = "wwwwaaadexxxxxxywww";

cout << encode(str);

return 0;

}

C

#include <stdio.h> #include <string.h>

// Function to implement run length encoding void encode(char *s) { char result[1000]; // assuming max size int k = 0; int n = strlen(s);

for (int i = 0; i < n; i++) {

    // Count occurrences of current character
    int count = 1;
    while (i < n - 1 && s[i] == s[i + 1]) {
        count++;
        i++;
    }

    // Append character and its count to result
    result[k++] = s[i];

    // convert count to string and append
    char temp[20];
    sprintf(temp, "%d", count);

    for (int j = 0; temp[j] != '\0'; j++) {
        result[k++] = temp[j];
    }
}

result[k] = '\0';

printf("%s", result);

}

// Driver code int main() { char str[] = "wwwwaaadexxxxxxywww";

encode(str);

return 0;

}

Java

import java.util.*;

class GFG {

// Function to implement run length encoding
static String encode(String s)
{
    String result = "";
    int n = s.length();

    for (int i = 0; i < n; i++) {

        // Count occurrences of current character
        int count = 1;
        while (i < n - 1 && s.charAt(i) == s.charAt(i + 1)) {
            count++;
            i++;
        }

        // Append character and its count to result
        result += s.charAt(i);
        result += Integer.toString(count);
    }

    return result;
}

public static void main(String[] args)
{
    String str = "wwwwaaadexxxxxxywww";

    System.out.println(encode(str));
}

}

Python

Function to implement run length encoding

def encode(s): result = "" n = len(s)

for i in range(n):

    # Count occurrences of current character
    count = 1
    while i < n - 1 and s[i] == s[i + 1]:
        count += 1
        i += 1

    # Append character and its count to result
    result += s[i]
    result += str(count)

return result

Driver code

str1 = "wwwwaaadexxxxxxywww"

print(encode(str1))

C#

using System;

class GFG {

// Function to implement run length encoding
static string encode(string s)
{
    string result = "";
    int n = s.Length;

    for (int i = 0; i < n; i++) {

        // Count occurrences of current character
        int count = 1;
        while (i < n - 1 && s[i] == s[i + 1]) {
            count++;
            i++;
        }

        // Append character and its count to result
        result += s[i];
        result += count.ToString();
    }

    return result;
}

public static void Main()
{
    string str = "wwwwaaadexxxxxxywww";

    Console.WriteLine(encode(str));
}

}

JavaScript

// Function to implement run length encoding function encode(s) { let result = ""; let n = s.length;

for (let i = 0; i < n; i++) {

    // Count occurrences of current character
    let count = 1;
    while (i < n - 1 && s[i] === s[i + 1]) {
        count++;
        i++;
    }

    // Append character and its count to result
    result += s[i];
    result += count.toString();
}

return result;

}

// Driver code let str = "wwwwaaadexxxxxxywww";

console.log(encode(str));

`