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.

   

解题思路：

   

   

   

屏幕剪辑的捕获时间: 2016/3/4 22:52

从左到右，两两进行比较。。。使用map和数组标记两种方式所消耗的时间不同。。

#include<string>

#include<iostream>

#include<map>

using namespace std;

class Solution {

public:

    int romanToInt(string s) {

        int n=s.size();

        if(n==0)return 0;

        // 68ms

        //map<char,int>m;

        //m['I']=1;

        //m['X']=10;

        //m['C']=100;

        //m['M']=1000;

        //m['V']=5;

        //m['L']=50;

        //m['D']=500;

   

        // 32ms

        int m[26]={0};

        m['I'-'A']=1;

        m['X'-'A']=10;

        m['C'-'A']=100;

        m['M'-'A']=1000;

        m['V'-'A']=5;

        m['L'-'A']=50;

        m['D'-'A']=500;

        int ans=0;

        for(int i=0;i<n-1;i++){

            int a=m[s[i]-'A'];

            if(s[i]=='I'||s[i]=='X'||s[i]=='C'){

            int b=m[s[i+1]-'A'];

            if(a<b)ans-=a;

            else

                ans+=a;

            }

            else

                ans+=a;

        }

        ans+=m[s[n-1]-'A'];

        return ans;

    }

};