Excel Sheet Column Number

Given a column title as appear in an Excel sheet, return its corresponding column number.

Example:

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28
...

Write your solution:

function main (col) {
    return;
}

function main (col) { return; }

Test Case 1

Input: "A"
Output: 1

Test Case 2

Input: "Z"
Output: 26

Test Case 3

Input: "AA"
Output: 27

Test Case 4

Input: "AB"
Output: 28

Test Case 5

Input: "ZY"
Output: 701

Solution

Complexity:

• Time complexity: O(n)
• Space complexity: O(1)

function main(col) {
    const letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
    const dict = Object.fromEntries(letters.split('').map((it, index) => [it, index + 1]));
    const lettersLen = letters.length;
    const colLen = col.length;

    return col
        .toUpperCase()
        .split('')
        .reduce((acc, letter, index) => acc + Math.pow(lettersLen, colLen - (index + 1)) * dict[letter], 0);
}