###### tags: `Leetcode` `easy` `string` `python` `c++`

# 171. Excel Sheet Column Number

## [題目來源:] https://leetcode.com/problems/excel-sheet-column-number/

## 題目:
Given a string columnTitle that represents the column title as appears in an Excel sheet, return its corresponding column number.

For example:

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

#### [圖片來源]: https://leetcode.com/problems/excel-sheet-column-number/

## 解題思路:
兄弟題目:參考 [168. Excel Sheet Column Title](/rt05Jg7TSwKYzNMFxfzY1Q)

* 此題為字母轉數字: 從頭逐一累加*26
* 注意
* python: **ord(' A ')=65**
* c++: **' 字母 '-'A'+1**

## Python:

class Solution(object):
    def titleToNumber(self, columnTitle):
        """
        :type columnTitle: str
        :rtype: int
        """
        #ord('A')=65
        res=0
        for i in range(len(columnTitle)):
            res*=26
            res+=ord(columnTitle[i])-64
        return res

if __name__ == '__main__':
    res = Solution()
    columnTitle = "AB"
    print(res.titleToNumber(columnTitle))

## C++:

#include<iostream>
using namespace std;
class Solution {
public:
    int titleToNumber(string columnTitle) {
        int res=0;
        //使用萬用auto
        for (auto val: columnTitle){
            res*=26;
            res+= (val-64);
        }
        return res;
        /*
        // sol2:
        for (int i=0; i<columnTitle.size(); i++){
            res*=26;
            res+= columnTitle[i]-'A'+1;
        }
        */

    }
};

int main(){
    Solution res;
    string columnTitle="AB";
    int ans=res.titleToNumber(columnTitle);
    cout<<ans<<endl;

    return 0;
}