The answer had come to him in a flash.

他一下子就有了答案。

It came to me in a flash of inspiration.

那是我灵机一动想到的。

He realised that he was doing it himself, and in a flash he understood the situation.

然后他意识到他自己在做这件事，刹那间他明白了情况。

A fortnight passed in a flash.

一晃半个月过去了。

Five years have elapsed in a flash.

一晃就是5年。