采用字符串的方法，格式为“aabbaadddc”。通过计算连续字母对字符串进行编码。例如：“a2b2a2d3c1”

I have written a code but i am not able to get the desired output. I am doing some mistake, but unable to trace what exactly it is. Below is my code.I have written a code but i am not able to get