0012. Integer to Roman (M)

Integer to Roman (M)

题目

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: 3
Output: "III"

Example 2:

Input: 4
Output: "IV"

Example 3:

Input: 9
Output: "IX"

Example 4:

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

Example 5:

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

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题意

将整数转化为指定格式的罗马数字。

思路

1. 直接打表，将每一位数字对应的罗马数字记录下来。
2. 依次减去[1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1]，并转化为罗马数字添加到字符串中。

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代码实现

Java

打表

class Solution {
    public String intToRoman(int num) {
        String[] single = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
        String[] tens = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
        String[] hundreds = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
        String[] thousands = {"", "M", "MM", "MMM"};
        return thousands[num / 1000] + hundreds[(num % 1000) / 100] + tens[(num % 100) / 10] + single[num % 10];
    }
}

减法

class Solution {
    public String intToRoman(int num) {
        String ans = "";
        int[] numeral = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
        String[] rome = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
        for (int i = 0; i < numeral.length; i++) {
            int count = num / numeral[i];
            num -= count * numeral[i];
            while (count > 0) {
                ans += rome[i];
                count--;
            }
        }
        return ans;
    }
}

JavaScript

/**
 * @param {number} num
 * @return {string}
 */
var intToRoman = function (num) {
  let res = ''
  let map = new Map([
    [1000, 'M'],
    [900, 'CM'],
    [500, 'D'],
    [400, 'CD'],
    [100, 'C'],
    [90, 'XC'],
    [50, 'L'],
    [40, 'XL'],
    [10, 'X'],
    [9, 'IX'],
    [5, 'V'],
    [4, 'IV'],
    [1, 'I'],
  ])

  map.forEach((value, key) => {
    res += value.repeat(Math.trunc(num / key))
    num %= key
  })

  return res
}