YoungProgrammer

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Problem 25: 
Consider the string ‘AAAABCCCCCDDDD’ consisting of alphabetic characters only. 
This string is of length 14. Since the string consists of alphabetic characters
only, duplicate characters can be removed and replaced with a duplication
factor n. With this technique the string can be compressed and represented 
by ‘4AB5C4D’.The compressed string is of length 7. Write a program which takes
a string in compressed form 
and recreates the original uncompressed string.

Note: The string will be of the format ‘nA...’ where n, the duplication factor, 
is an integer between 2 and 99 and A is an uppercase alphabetic character.

Input:3A4B7D
output:AAABBBBDDDDDDD
Input: 2BA3C
Output: BBACCC

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

char input[100];

void Process() {
    int i, j, pre = 0;
    for(i = 0; input[i]; ) {
        if(isalpha(input[i])) {
           if(pre == 0) pre = 1; // why ? consider input 2BA3C where 'A' is given once but 1 is not in the input
           for(j = 0; j<pre; j++) {
              printf("%c",input[i]);
           }
           i++;
           pre = 0;
           continue;
        }else if(isdigit(input[i])) {
           pre = pre*10 + input[i] - '0';
           i++;     
        }
    }
}
int main() {
    gets(input);
    Process();
    return 0;
}

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