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题目： You are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what the number is. Each 阅读全文
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题目： Given two strings s and t, determine if they are isomorphic. Two strings are isomorphic if the characters in s can be replaced to get t. All occur 阅读全文
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题目：Given an integer, write a function to determine if it is a power of three. Follow up: Could you do it without using any loop / recursion? 题目解答：本题是不 阅读全文