0x00 问题描述

Roman numerals are represented by seven different symbols: I, V, X, L, C, D, and M.
罗马数字以下列字母组成

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, “two” is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty-seven is written as XXVII, which is XX + V + II.
例如，数字2的罗马数字为II，相当于两个1相加。12则以XII表示,24的罗马数字为XXVII，相当于XX+V+II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:
罗马数字顺序是从左到右，最左边是最大值，最右为最小值。然而阿拉伯数字4并不是以IIII来表示，罗马数字中的4是以IV表示的。同样9对应的是IV。

I can be placed before V (5) and X (10) to make 4 and 9.
X can be placed before L (50) and C (100) to make 40 and 90.
C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.
系统将输入一个罗马数字，将其转化为阿拉伯数字整数输出。该输入的范围将被限制在1-3999

Example:

Input: "III"
Output: 3

Input: "IV"
Output: 4

Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

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0x00 问题描述

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.
判断一个整数是否为palindrome (如果一个整数正序等于倒序则是palindrome)

Example:

Input: 121
Output: true

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

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0x00 问题描述

Given a 32-bit signed integer, reverse digits of an integer.
已知输入是一个32位的整数，将其进行十进制倒序

Example:

Input: 123
Output: 321

Input: -123
Output: -321

Input: 120
Output: 21

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0x00 问题描述

Given an array of integers, return indices of the two numbers such that they add up to a specific target.
已知一组整数，返回两个整数的索引值，两个整数相加必须等于给定目标整数

You may assume that each input would have exactly one solution, and you may not use the same element twice.
假设只有一种答案的可能且每个数字只能使用一次，既不能重复相加。

Example:

Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

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