Grothendieck said

"Since then I’ve had the chance in the world of mathematics that bid me welcome, to meet quite a number of people, both among my “elders” and among young people in my general age group who were more brilliant, much more ‘gifted’ than I was. I admired the facility with which they picked up, as if at play, new ideas, juggling them as if familiar with them from the cradle–while for myself I felt clumsy, even oafish, wandering painfully up an arduous track, like a dumb ox faced with an amorphous mountain of things I had to learn (so I was assured) things I felt incapable of understanding the essentials or following through to the end. Indeed, there was little about me that identified the kind of bright student who wins at prestigious competitions or assimilates almost by sleight of hand, the most forbidding subjects.

In fact, most of these comrades who I gauged to be more brilliant than I have gone on to become distinguished mathematicians. Still from the perspective or thirty or thirty five years, I can state that their imprint upon the mathematics of our time has not been very profound. They’ve done all things, often beautiful things in a context that was already set out before them, which they had no inclination to disturb. Without being aware of it, they’ve remained prisoners of those invisible and despotic circles which delimit the universe of a certain milieu in a given era. To have broken these bounds they would have to rediscover in themselves that capability which was their birthright, as it was mine: The capacity to be alone."

java dotnet idiocy

[ArgumentException: An item with the same key has already been added.]
   System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +52
   System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +10571237
   BlogEngine.Core.AuthorProfile.get_Profiles() +244
   BlogEngine.Core.AuthorProfile.GetProfile(String username) +44
   BlogEngine.Core.Post.get_AuthorProfile() +8
   post.OnInit(EventArgs e) +1841
   System.Web.UI.Control.InitRecursive(Control namingContainer) +134
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +489

Every line is precious.

Insert(TKey key, TValue value, Boolean add)
GetProfile(String username) calls get_Profiles()
InitRecursive
Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint
System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)

вот еще задача с интервью

Бинарное дерево с целыми числами в узлах, неповторяющимися, обойдено in-order и pre-order; имеем два массива. Восстановите дерево.

Не ахти, но миленькая.
Вариант - сделайте n log n