两句都正确的.
第一句是把did not分开写的,而第二句是把did not连在一起写的.
个人认为,第二句更常用的.
如：
Why didn't you leave yesterday?
要比
Why did you not leave yesterday?更常见,更口语化.
还有许多的：
do not ——don't
does not——doesn't
will not——won't
shall not——shan't
can not——can't