Question

needn't have done和didn't need to do 有什么不同

Answer 1

needn't have done是表示有后悔的含义，意味本不该做什么事（但是那个事已经做过了）；didn't need to do没有这个意思，即不必要做的事情已经做或没做过并没有明确的确认。

Answer 2

needn't have done
不必做
I dressed very warmly for the trip, but I needn't have done so.the weather was hot.
旅行时，我衣服穿得较多，其实没有必要。那时天很热。

didn't need to do
不需要做
I didn't need to see his expression.All I had to do was listen.
我无需看他的表情。我只需聆听他的声音。

Answer 3

本不必做某事
不必做某事

追答

时态不一样，表达的意思也就不同