## Question

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
...
```

**Example 1:**

```
Input: columnTitle = "A"
Output: 1
```

**Example 2:**

```
Input: columnTitle = "AB"
Output: 28
```

**Example 3:**

```
Input: columnTitle = "ZY"
Output: 701
```

**Constraints:**

`1 <= columnTitle.length <= 7`

`columnTitle`

consists only of uppercase English letters.`columnTitle`

is in the range`["A", "FXSHRXW"]`

.

## Approach

- Same idea with question 168 and this question is easier to implement.
- Each digit of column title string is the coefficient of the entire number for each base.

## Code

class Solution { public int titleToNumber(String columnTitle) { int res = 0; int temp = 1; for (int i = columnTitle.length() - 1; i >= 0; i--) { char ch = columnTitle.charAt(i); int sum = temp * (ch - 'A' + 1); temp *= 26; res += sum; } return res; } }