## 0x00 问题描述

Roman numerals are represented by seven different symbols: I, V, X, L, C, D, and M.

``````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.

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:

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.

# 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.

# 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.

# 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.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

# Example:

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

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