[leetcod] 12. Integer to Roman

[leetcod] 12. Integer to Roman

Description

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

Example 1:

Input: 3Output: "III"

Example 2:

Input: 4Output: "IV"

Example 3:

Input: 9Output: "IX"

Example 4:

Input: 58Output: "LVIII"Explanation: L = 50, V = 5, III = 3.

Example 5:

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

分析

题目的意思是：把一个整数变为一个罗马数字。

规则

相同的数字连写， 所表示的数等于这些数字相加得到的数。如 XXX表示 30小的数字在大的数字的右边， 所表示的数等于这些数字相加得到的数 如VIII 表示8小的数字(限于I, X, C)在大的数字的左边， 所表示的数等于大数减去小的数： 如IV 表示4在一个数的上面画一条横线， 表示这个数增值1000倍(由于题目只考虑4000以内的数，所以这条规则不用考虑)。

五个组数规则

I, X, C： 最多只能连用3个， 如果放在大数的左边，只能用1个。V, L, D: 不能放在大数的左边，只能使用一个。I 只能用在V和X的左边。 IV表示4, IX表示9X只能放在L,C左边。 XL 表示40, XC表示90C只能用在D, M左边。 CD 表示400, CM表示900

代码

class Solution {public: string intToRoman(int num) { string res=""; vector key={1000,900,500,400,100,90,50,40,10,9,5,4,1}; vector value={"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"}; for(int i=0;i

参考文献

​​[编程题]integer-to-roman​​​​leetcode 罗马数字与整数的转换算法​​​​利用Markdown创建表格​​

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