#include <stdlib.h>
#include <string.h>
#include <stdio.h>
 
int main()
{
    char symbols[16] = "";
    char symbols_copy[16];
    int index = 0;
    while (index++ < 15)
    {
         memcpy(symbols_copy, symbols, sizeof(symbols));
 
         if (index % 2)
             snprintf(symbols, sizeof symbols, "a%s", symbols_copy);
         else
             snprintf(symbols, sizeof symbols, "b%s", symbols_copy);
 
         printf("%s\n", symbols);
    }
    return 0;
}
 

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