LeetCode : Roman to Integer [java]

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

思路：记住这种算法，后边的比前边的大，加上后边数-2*前边的数，否则，直接加上后边的数。

public class Solution {public int romanToInt(String s) {int ret = toNumber(s.charAt(0));for (int i = 1; i < s.length(); i++) {if (toNumber(s.charAt(i - 1)) < toNumber(s.charAt(i))) {ret += toNumber(s.charAt(i)) - 2 * toNumber(s.charAt(i - 1));} else {ret += toNumber(s.charAt(i));}}return ret;}private int toNumber(char ch) {switch (ch) {case 'I':return 1;case 'V':return 5;case 'X':return 10;case 'L':return 50;case 'C':return 100;case 'D':return 500;case 'M':return 1000;}return 0;}}