【轉(zhuǎn)貼】google的一道面試題,有能力就施展下吧！

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onsider a function which, for a given whole number n,

returns the number of ones required when writing out all numbers between 0 and n.

For example, f(13)=6. Notice that f(1)=1. What is the next largest n such that f(n)=n?


翻譯：有一個(gè)整數(shù)n,寫(xiě)一個(gè)函數(shù)f(n),返回0到n之間出現(xiàn)的"1"的個(gè)數(shù)。比如f(13)=6,現(xiàn)在f(1)=1,問(wèn)下一個(gè)最大的f(n)=n的n是什么？