171. Excel Sheet Column Number

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 
    ...

Example 1:

Input: "A"
Output: 1

Example 2:

Input: "AB"
Output: 28

Example 3:

Input: "ZY"
Output: 701

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是LeetCode Excel Sheet Column Title的反过程，要把字符串转换为数字，比前一题简单，扫一遍字符串，和’A’作差，然后结果不断乘26。完整代码如下：

class Solution {
public:
    int titleToNumber(string s)
    {
        int ans = 0;
        for (int i = 0; i < s.size(); i++) {
            ans = ans * 26 + (s[i] – ‘A’) + 1;
        }
        return ans;
    }
};

本代码提交AC，用时3MS。