When applying for some to cross office of congress plan division at the outset, I encountered a very strange problem: A flock of people fly ball, there is a hat on every poll. The cap has only black and white two kinds, black have at least. Everybody can see the color of someone else cap, do not know oneself however. Compere lets everybody see the what hat that wears on people head first, black out next, if somebody thinks what he wears is black hat, hit oneself an a slap on the face. Black out for the first time, without sound. Then reopen lamp, everybody looks again, when blacking out, still not even a crow or sparrow can be heard. Arrive the 3rd times to black out all the time, just the acoustical sound that breaks off slap sb in the face of the bang that break off bang rises. Ask how many person is wearing black hat? 　　

Hear an issue, I am dizzy. White hat of what black hat opens the lamp to black out, do this answer how possibly reach? How to do? My cerebra a blank... 　

Gave examination room to ask ability knows, so this is the logistic problem of line model, secret must make a hypothesis in you. If only a person wears black hat, then he sees everybody wears white hat, answer when blacking out for the first time from slap sb in the face, so should more than a person wears black hat; If have two black hats, two people see first time only the black hat on head of the other side, dare not decide oneself color, but black out to the 2nd, this two people should be reasonable, if oneself are wearing white hat, that the other side is in early answer last time slap sb in the face, what wear because of this oneself also is black hat -- ― also can have a slap on the face ring then; But the fact is sound of a slap on the face since ability noise the 3rd, demonstrative full-court is more than two black hats, the rest may be deduced by analogy, should be to involve the lamp a few times, have a few black hats. 　　

Old day! The family helped me tell 10 minutes, I just understand, this kind of problem, even if killed me, also answer not to come out. 　　

Clew: Take an examination of an official " tangle hard " so far, you also rely on actual strength to be fought with him only. Allegedly this is the reservation title of certain big company, can change his appearance every year, smoke a few hapless eggs to take an examination of casually. E.g. , "Have a courtyard in stayed in a lot of families, every have a dog. Suddenly the dog was gotten hydrophobic, you are taking a gun to look in the window, can see the dog that fastens the home has disease only. The first day of gun did not ring, had not rung the following day, the 3rd day rang eventually. Ask have how many dog mad... " (origin: Happy event is full you)

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