13-roman-to-integer

题目描述：

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 1:

Input: "III"
Output: 3

Example 2:

Input: "IV"
Output: 4

Example 3:

Input: "IX"
Output: 9

Example 4:

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

Example 5:

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

代码解答：

package com.jack.algorithm;

import java.util.HashMap;
import java.util.Map;

/**
 * create by jack 2018/10/27
 *
 * @author jack
 * @date: 2018/10/27 08:20
 * @Description:
 * 罗马数字转换为整数
 */
public class RomanToInteger {

    /**
     * 题目描述：
     * https://leetcode.com/problems/roman-to-integer/
     *
     *
     * @param s
     * @return
     */
    public static int romanToInt(String s) {
        //为空则直接返回0
        if (s.isEmpty()) {
            return 0;
        }
        int length = s.length();
        int sum = 0;
        Map<Character, Integer> charIntMap = getCharInt();
        //如果为1，则直接获取
        if (length == 1) {
            sum += charIntMap.get(s.charAt(0));
        }
        //如果大于1，长度为2以上
        if (length > 1) {
            //4 or 9
            if (s.charAt(0) == 'I'&& (s.charAt(1) == 'V' ||s.charAt(1) == 'X')) {
                sum += charIntMap.get(s.charAt(1)) - charIntMap.get(s.charAt(0));
                if (length > 2) {
                    sum +=romanToInt(s.substring(2));
                }
                //40 or 90
            } else if (s.charAt(0) == 'X' &&(s.charAt(1) == 'L' ||s.charAt(1) == 'C')) {
                sum += charIntMap.get(s.charAt(1)) - charIntMap.get(s.charAt(0));
                if (length > 2) {
                    sum +=romanToInt(s.substring(2));
                }
                //400 or 900
            }else if (s.charAt(0) == 'C' &&(s.charAt(1) == 'D' ||s.charAt(1) == 'M')) {
                sum += charIntMap.get(s.charAt(1)) - charIntMap.get(s.charAt(0));
                if (length > 2) {
                    sum +=romanToInt(s.substring(2));
                }
            } else {
                sum += charIntMap.get(s.charAt(0));
                sum += romanToInt(s.substring(1));
            }
        }
        return sum;
    }

    public static Map<Character, Integer> getCharInt(){
        Map<Character, Integer> intCharMap = new HashMap<Character, Integer>(16);
        intCharMap.put('I', 1);
        intCharMap.put('V', 5);
        intCharMap.put('X', 10);
        intCharMap.put('L', 50);
        intCharMap.put('C', 100);
        intCharMap.put('D', 500);
        intCharMap.put('M', 1000);
        return intCharMap;
    }

    public static void main(String[] args) {
        //int sum = romanToInt("III");
        //int sum = romanToInt("IV");
        //int sum = romanToInt("IX");
        //int sum = romanToInt("LVIII");
        int sum = romanToInt("DCXXI");
        System.out.println("sum="+sum);
    }
}

源代码地址：

源码