leetcode--171 Excel Sheet Column Number

Related to question Excel Sheet Column Title

Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

    A -> 1
    B -> 2
    C -> 3
    ...
    Z -> 26
    AA -> 27
    AB -> 28 

Credits:

Special thanks to @ts for adding this problem and creating all test cases.

/// 相当于是26进制 

例如 AA=1*26+1;  AB=1*26+2   ;  BA=2*26+1=53;

class Solution {
public:
    int titleToNumber(string s) {
        int n=s.length(),i,s1='A';
        for(i=0;i<n;i++)
        {
            s1=(s1-'A')*26+s[i]-'A'+1;
            s1=s1+'A';
        }
        return s1-'A';
    }
};