LeetCode 171. Excel Sheet Column Number

Description

Given a 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

Analysis

It’s almost a base-26 system, but the range should be 1~26 instead of 0~25 for every symbol.

Code

class Solution {
public:
int titleToNumber(string s) {
int factor = 1, sum = 0;
sum += s[s.size() - 1] - 64;
for(int i = s.size()-2; i >= 0; i--){
factor *= 26;
sum += factor * (s[i] - 64);
}
return sum;
}
};

Appendix

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

Run Time: 3ms