LeetCode 258: Add Digits

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

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LeetCode 69: Sqrt(x)

Implement int sqrt(int x). Compute and return the square root of x.

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Implement pow(x, n).

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Reverse digits of an integer. Example1: x = 123, return 321 Example2: x = -123, return -321.

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Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999.

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There are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb.

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Determine whether an integer is a palindrome. Do this without extra space.

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这个题跟Power of Three的思路基本一模一样，解法也差不多。但是因为是2啊，毕竟是计算机的进制数，所以&,|这些位操作总能出奇迹。