Possibile Soluzione Problema 1

def decompression(str):
# @param str : string (compressa)
# @return string (str decompressa)
    res=''
    for i in range(0,len(str)):
        char=str[i]
        if char.isdigit():
           res=res+(int(char)-1)*str[i+1]
        else:
           res=res+char
    return res

def compression(str):
# @param str : string (decompressa e composta esclusivamente da caratteri alfabetici)
# @return string (str compressa)
    res=''
    count=1
    for i in range(0,len(str)):
        char=str[i]
        if char==str[min(i+1,len(str)-1)]:
           if i==len(str)-1 and count!=2 and count!=1:
              res=res+repr(count)+char
              return res
           elif i==len(str)-1 and count==2:
              res=res+count*char
              return res
           elif i==len(str)-1 and count==1:
              res=res+char
              return res
           count=count+1
        elif char!=str[min(i+1,len(str)-1)] and count!=2 and count!=1:
           res=res+repr(count)+char
           count=1
        elif count==2:
           res=res+count*char
           count=1
        elif count==1:
           res=res+char
    return res