it seems i have understood you. you may have solved the problem

來源: 皆兄弟也 於 2010-06-17 10:48:31 [] [博客] [舊帖] [給我悄悄話] 閱讀數 : (192 bytes)

my explanation use a list of n+N-1 symbols, you break it into two segments as two sides of a n x N rectangle. I think once you arrive this point, you must have solved the problem. C(n+N-1, n)

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