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Run Length Encoding and Decoding

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  • Difficulty Level : Easy
  • Last Updated : 16 Jun, 2022
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Given an input string, write a function that returns the Run Length Encoded string for the input string.
For example, if the input string is “wwwwaaadexxxxxx”, then the function should return “w4a3d1e1x6”

Recommended Practice

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++




// CPP program to implement run length encoding
#include <bits/stdc++.h>
using namespace std;
 
void printRLE(string str)
{
    int n = str.length();
    for (int i = 0; i < n; i++) {
 
        // Count occurrences of current character
        int count = 1;
        while (i < n - 1 && str[i] == str[i + 1]) {
            count++;
            i++;
        }
        // Print character and its count
        cout << str[i] << count;
    }
}
//Driver code
int main()
{
    string str = "wwwwaaadexxxxxxywww";
    printRLE(str);
    return 0;
}


C




#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_RLEN 50
 
/* Returns the Run Length Encoded string for the
   source string src */
char* encode(char* src)
{
    int rLen;
    char count[MAX_RLEN];
    int len = strlen(src);
 
    /* If all characters in the source string are different,
    then size of destination string would be twice of input string.
    For example if the src is "abcd", then dest would be "a1b1c1d1"
    For other inputs, size would be less than twice.  */
    char* dest = (char*)malloc(sizeof(char) * (len * 2 + 1));
 
    int i, j = 0, k;
 
    /* traverse the input string one by one */
    for (i = 0; i < len; i++) {
 
        /* Copy the first occurrence of the new character */
        dest[j++] = src[i];
 
        /* Count the number of occurrences of the new character */
        rLen = 1;
        while (i + 1 < len && src[i] == src[i + 1]) {
            rLen++;
            i++;
        }
 
        /* Store rLen in a character array count[] */
        sprintf(count, "%d", rLen);
 
        /* Copy the count[] to destination */
        for (k = 0; *(count + k); k++, j++) {
            dest[j] = count[k];
        }
    }
 
    /*terminate the destination string */
    dest[j] = '\0';
    return dest;
}
 
/*driver program to test above function */
int main()
{
    char str[] = "wwwwaaadexxxxxxywww";
    char* res = encode(str);
    printf("%s", res);
    getchar();
}


Java




/*package whatever //do not write package name here */
 
import java.io.*;
public class GFG {
 
    public static void encoding(String str)
    {
        int n = str.length();
        for (int i = 0; i < n; i++) {
 
            // Count occurrences of current character
            int count = 1;
            while (i < n - 1
                   && str.charAt(i) == str.charAt(i + 1)) {
                count++;
                i++;
            }
 
            // Print character and its count
            System.out.print(str.charAt(i) + "" + count);
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
 
        String str = "wwwwaaadexxxxxxywww";
        encoding(str);
    }
}


Python3




# Python3 program to implement
# run length encoding
def printRLE(st):
 
    n = len(st)
    i = 0
    while i < n- 1:
 
        # Count occurrences of
        # current character
        count = 1
        while (i < n - 1 and
               st[i] == st[i + 1]):
            count += 1
            i += 1
        i += 1
 
        # Print character and its count
        print(st[i - 1] +
              str(count),
              end = "")
 
# Driver code
if __name__ == "__main__":
 
    st = "wwwwaaadexxxxxxywww"
    printRLE(st)
 
# This code is contributed by Chitranayal


C#




// C# program to implement run length encoding
using System;
class GFG
{
public class RunLength_Encoding
{
    public static void printRLE(String str)
    {
        int n = str.Length;
        for (int i = 0; i < n; i++)
        {
 
            // Count occurrences of current character
            int count = 1;
            while (i < n - 1 && str[i] == str[i + 1])
            {
                count++;
                i++;
            }
 
            // Print character and its count
            Console.Write(str[i]);
            Console.Write(count);
        }
    }
 
    public static void Main(String[] args)
    {
        String str = "wwwwaaadexxxxxxywww";
        printRLE(str);
    }
}
}
 
// This code is contributed by shivanisinghss2110


Javascript




<script>
// Javascript program to implement run length encoding
    function printRLE(str)
    {
        let n = str.length;
        for (let i = 0; i < n; i++)
        {
            // Count occurrences of current character
            let count = 1;
            while (i < n - 1 && str[i] == str[i+1])
            {
                count++;
                i++;
            }
             
            // Print character and its count
            document.write(str[i]);
            document.write(count);
        }
    }
     
    let str = "wwwwaaadexxxxxxywww";
    printRLE(str);
     
    // This code is contributed by rag2127
</script>


Output

w4a3d1e1x6y1w3

Time Complexity: O(n)
Auxiliary Space: O(1)

Please write comments if you find the above code/algorithm incorrect, or find better ways to solve the same problem.


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