Compressing a String - An Amazon Problem

Problem Statement : 

Compress a given string "aabbbccc" to "a2b3c3" constraint: inplace compression, no extra space to be used  assumption : output size will not exceed input size.. ex input:"abb" -> "a1b2" buffer overflow.. such inputs will not be given.

Solution : 

Since no extra is to be use hence we can't use recursion in this case . we need to operate on array to make the operation in place . lets see a simple solution to this problem though many ways of doing it possible so one of them I am mentioning here : 

public  static String compressString(String input){

/*

* @sachin srivastava

* tek9g.blogspot.com

* */

StringBuilder sb = new StringBuilder();

if(input == null || input.isEmpty()){

return null;

} else if(input.length() <= 2){

return input;

}

char[] ch = input.toCharArray();

int lenght = ch.length;

int count = 1;

for (int i = 0; i <=lenght-1; i++) {

if(i!=lenght-1 && ch[i] == ch[i+1] ){

count++;

} else {

sb.append(ch[i] + "" +count);

count = 1;

}

}

if(input.length() < sb.toString().length()){

System.out.println("invalid input buffer overflow");

}

return sb.toString();

}

Input1 : aaaaaaaabbcccccccgggggggaaaaaaaeeeeeef

Output1 : a8b2c7g7a7e6f1

Input2 :  abb

Output : invalid input buffer overflow

a1b2

Input3 : abbrrrrtttttgggaaawwww

Output3 : a1b2r4t5g3a3w4

Time Complexity : O(n)

Space Complexity : O(1)  -- in place 

Enjoy coding !!!!