LeetCode:171. Excel表列序號

class Solution {
public:
    int titleToNumber(string s) {
        map<char,int> m;

        m['A']=1;
        m['B']=2;
        m['C']=3;
        m['D']=4;
        m['E']=5;
        m['F']=6;
        m['G']=7;
        m['H']=8;
        m['I']=9;
        m['J']=10;
        m['K']=11;
        m['L']=12;
        m['M']=13;
        m['N']=14;
        m['O']=15;
        m['P']=16;
        m['Q']=17;
        m['R']=18;
        m['S']=19;
        m['T']=20;
        m['U']=21;
        m['V']=22;
        m['W']=23;
        m['X']=24;
        m['Y']=25;
        m['Z']=26;
        int res=0;
        for(int i=0;i<s.size();i++)
        {
            res=res*26+m[s[i]];
        }
        return res;
    }
};