how did make code decompress java spring boot? : Hi everyone i'm Starting Beginner learning java springboot .my profressor give an assignment for me . that's decompress java springboot. the proposition has define input and out . following example

Input1 : 2[abc]3[ab]c
Output1 : abcabcabababc

Input2 : 10[a]c2[ab]
Output2 : aaaaaaaaaacabab

Input3 : 2[3[a]b]
Output3 : aaabaaab

somebody help me please . that's very seriousry for me . can help and explain to me T_T