Roman to Integer

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题目

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

方法

    public int romanToInt(String s) {        HashMap<String, Integer> hm = new HashMap<String, Integer>();        hm.put("I", 1);        hm.put("II", 2);        hm.put("III", 3);        hm.put("IV", 4);        hm.put("V", 5);        hm.put("VI", 6);        hm.put("VII", 7);        hm.put("VIII", 8);        hm.put("IX", 9);        hm.put("X", 10);        hm.put("XX", 20);        hm.put("XXX", 30);        hm.put("XL", 40);        hm.put("L", 50);        hm.put("LX", 60);        hm.put("LXX", 70);        hm.put("LXXX", 80);        hm.put("XC", 90);        hm.put("C", 100);        hm.put("CC", 200);        hm.put("CCC", 300);        hm.put("CD", 400);        hm.put("D", 500);        hm.put("DC", 600);        hm.put("DCC", 700);        hm.put("DCCC", 800);        hm.put("CM", 900);        hm.put("M", 1000);        hm.put("MM", 2000);        hm.put("MMM", 3000);        int len = s.length();        int num = 0;        String currentStr = "";        String preStr = "";        for(int i = 0; i < len; i ++){            char ch = s.charAt(i);            currentStr = preStr + ch;            if(hm.containsKey(currentStr)){                preStr = currentStr;            }else{                num = num + hm.get(preStr);                preStr = "" + ch;            }        }        num = num + hm.get(preStr);        return num;    }

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