Excel Sheet Column Number

Problem

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
...

Constraints

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

Solution

The problem Excel Sheet Column Number can be solved using the technique from Excel Sheet Column Title except reverse.

Implementation

class Solution
{
  public:
    int titleToNumber(string columnTitle)
    {
        int ret = 0;
        long mul = 1;

        for (int i = columnTitle.length() - 1; i >= 0; i--)
        {
            ret += mul * (columnTitle[i] - 'A' + 1);
            mul *= 26;
        }

        return ret;
    }
};