CompressDecompress

Main.java

package com.company;

public class Main {
    String str;
    String compStr;
    Main(String str){
        this.str=str;
    }
    //Str => aaaabbcdddddeeeeeeffffghhhhh
    String compress(){
        StringBuffer buff = new StringBuffer();
        //buff.append(str.charAt(0));
        char c = str.charAt(0);
        int runningCount=0;
        runningCount++;
        //Master loop to compress in O(n)
        for(int i=1;i<str.length();i++){
           //This is an important condition to emit count of last character
           if(i==str.length()-1)
               buff.append(c+""+runningCount);
           else if(str.charAt(i)==c)
               runningCount++;
           else{
               buff.append(c+""+runningCount);
               //Reset running count;
               runningCount=1;
           }
           c = str.charAt(i);
        }
        return buff.toString();
    }
    String decompress(String compressedString){
     int i;int x;x=0;
        StringBuffer buff = new StringBuffer();
        for(i=0;i<compressedString.length();i++)
        {
            char c;
            int count;
            c= compressedString.charAt(i);
            count = Character.getNumericValue(compressedString.charAt(i+1));
            while(x<count){
                buff.append(c);
                x++;
            }x=0;
            i++;
        }
     return buff.toString();
    }
    public static void main(String[] args) {
        Main obj = new Main("xaaaabbcdddddeeeeeeffffghhhhhassserer");
        String str = obj.compress();
        System.out.println(str);
        System.out.println(obj.decompress(str));
    }
}