LeetCode-12. Integer to Roman-13. Roman to Integer
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12. Integer to Roman
Given an integer, convert it to a roman numeral.
Input is guaranteed to be within the range from 1 to 3999.
将一个int型的数字转化为罗马数字,范围在1-3999。下面是罗马数字的介绍及基本规则:
罗马数字采用七个罗马字母作数字、即Ⅰ(1)、X(10)、C(100)、M(1000)、V(5)、L(50)、D(500)。记数的方法:
- 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 Ⅲ=3
- 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=8、Ⅻ=12
- 小的数字(限于 Ⅰ、X 和 C)在大的数字的左边,所表示的数等于大数减小数得到的数,如 Ⅳ=4、Ⅸ=9
注意点:
- 基本数字 Ⅰ、X 、C 中的任何一个、自身连用构成数目、或者放在大数的右边连用构成数目、都不能超过三个,放在大数的左边只能用一个
- 不能把基本数字 V 、L 、D中的任何一个作为小数放在大数的左边采用相减的方法构成数目,放在大数的右边采用相加的方式构成数目时只能使用一个
- V 和 X 左边的小数字只能用 Ⅰ
- L 和 C 左边的小数字只能用 X
- D 和 M 左边的小数字只能用 C
解题思路
根据上面的规则和注意点可以看出,罗马字符及其组合能代表的数字有:
package solutions._12;/** * 12. Integer to Roman */class Solution { public String intToRoman(int num) { /** * "M" "CM" "D" "CD" "C" "XC" "L" "XL" "X" "IX" "V" "IV" "I" * 1000 900 500 400 100 90 50 40 10 9 5 4 1 */ StringBuilder sb = new StringBuilder(); String symbol[] = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"}; int value[] = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1}; for (int i = 0; num != 0; i++) { while (num >= value[i]) { num -= value[i]; sb.append(symbol[i]); } } return sb.toString(); } public String intToRoman2(int num) { //1000 2000 3000 String M[] = {"", "M", "MM", "MMM"}; //100 200 300 400 500 600 700 800 900 String C[] = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"}; //10 20 30 40 50 60 70 80 90 String X[] = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"}; //1 2 3 4 5 6 7 8 9 String I[] = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"}; return M[num / 1000] + C[(num % 1000) / 100] + X[(num % 100) / 10] + I[num % 10]; } public static void main(String[] args) { Solution solution = new Solution(); for (int i = 1; i <= 1000; i++) { System.out.println(i + ":" + solution.intToRoman(i)); } }}
13. Roman to Integer
Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.
package solutions._13;import java.util.HashMap;import java.util.Map;/** * 13. Roman to Integer */public class Solution { private Map<Character, Integer> map = new HashMap<>(); public Solution() { map.put('I', 1); map.put('V', 5); map.put('X', 10); map.put('L', 50); map.put('C', 100); map.put('D', 500); map.put('M', 1000); } public int romanToInt(String s) { char[] arr = s.toCharArray(); int result = 0; for (int i = 0; i < arr.length; i++) { int val = map.get(arr[i]); if (i == arr.length - 1 || map.get(arr[i + 1]) <= map.get(arr[i])) { result += val; } else { result -= val; } } return result; } public static void main(String[] args) { Solution solution = new Solution(); System.out.println(solution.romanToInt("VIII")); }}
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