# 171. Excel Sheet Column Number

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

## problem

> 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 
...
```

## example

```
Example 1:

Input: columnTitle = "A"
Output: 1

Example 2:

Input: columnTitle = "AB"
Output: 28

Example 3:

Input: columnTitle = "ZY"
Output: 701

Example 4:

Input: columnTitle = "FXSHRXW"
Output: 2147483647


Constraints:
-  1 <= columnTitle.length <= 7
-  columnTitle consists only of uppercase English letters.
-  columnTitle is in the range ["A", "FXSHRXW"].
```

## solution

```
/**
 * 26 进制表示 
 * 26-based express
 */
class Solution {
    public int titleToNumber(String columnTitle) {
        int ret = 0;
        for(char c: columnTitle.toCharArray()) {
            ret = ret * 26 + (int)(c - 'A' + 1);
        }
        return ret;
    }
}
```