一、题目

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
…

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”].

二、题解

class Solution {
public:int titleToNumber(string columnTitle) {int n = columnTitle.size();int res = 0;long long mul = 1;for(int i = n - 1;i >= 0;i--){int k = columnTitle[i] - 'A' + 1;res += k * mul;mul *= 26;}return res;}
};