Roman to Integer (Easy)

Description

Given a roman numeral, convert it to an integer.

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

Analysis

罗马数字转换成数字。因为肯定是非递增的，突然递增的情况下就是相减

My Solution

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//C++
class Solution {
    int checknum(char c){
        if(c=='I')  return 1;
        if(c=='V')  return 5;
        if(c=='X')  return 10;
        if(c=='L')  return 50;
        if(c=='C')  return 100;
        if(c=='D')  return 500;
        if(c=='M')  return 1000;
        return 0;
    }
public:
    int romanToInt(string s) {
        int ans = 0,pre;
        for(int i=(int)s.length()-1;i>=0;i--){
            if(ans==0){
                pre = checknum(s[i]);
                ans+=pre;
            }
            else{
                int now = checknum(s[i]);
                ans+=now*(now>=pre?1:-1);
                pre = now;
            }
        }
        return ans;
    }
};