Add homework 5 starter file

Signed-off-by: kfei <kfei@kfei.net>
Solve problem 1 to 3 for homework 5

Signed-off-by: kfei <kfei@kfei.net>
Solve problem 4 and 5 for homework 5

Signed-off-by: kfei <kfei@kfei.net>
Finish challenge problems for homework 5

Signed-off-by: kfei <kfei@kfei.net>