# 171. Excel Sheet Column Number

### Leetcode

<https://leetcode.com/problems/excel-sheet-column-number/>

### 題目

Given a string `columnTitle` that represents the 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 
...
```

### 解答 <a href="#ti-jie" id="ti-jie"></a>

* **方法一**

```
// 'A'.charCodeAt(0) === 65;

var titleToNumber = function(columnTitle) {
    let res = 0;
    for(let i=0; i<columnTitle.length; i++) {
        const factor = columnTitle.length - 1 - i;
        res += (columnTitle.charCodeAt(i) - 64) * (factor ? 26 ** factor : 1);
    }
    return res;
};
```

Runtime: 88 ms, faster than 74.43% of JavaScript online submissions for Excel Sheet Column Number.

Memory Usage: 40.4 MB, less than 31.92% of JavaScript online submissions for Excel Sheet Column Number.

### 測資

```
let columnTitle = 'AB'; // 27
columnTitle = 'AZ'; // 52
columnTitle = "ZY"; // 701
columnTitle = "FXSHRXW"; // 2147483647

console.log(titleToNumber(columnTitle))
```
