171. Excel Sheet Column Number

171. Excel Sheet Column Number

1 Description #

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

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"].

2 Solution #

class Solution {
public:
  int titleToNumber(string columnTitle) {
    // Time complexity: O(N), N is the size of columnTitle
    // Space complexity: O(1)
    int size = columnTitle.size();
    long result = 0;
    for(int i = 0; i < size; i++){
      result = result * 26 + columnTitle[i] - 'A' + 1;
    }
    return result;
  }
};