LeetCode August - Day 10

Problem Statement

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 
    ...

Example 1:

Input: "A"
Output: 1

Example 2:

Input: "AB"
Output: 28

Example 3:

Input: "ZY"
Output: 701

Constraints:

1 <= s.length <= 7
s consists only of uppercase English letters.
s is between “A” and “FXSHRXW”.

Inputs, Outputs, Constraints & Exceptions

• I: string
• O: number
• C: - s.length in range [1,7]
  • chars are BASIC ASCII uppercase chars
  • s is between “A” and “FXSHRXW”
• E: - s.length is 1
  • s is “FXSHRXW”

Code

/**
 * @param {string} s
 * @return {number}
 */
function titleToNumber(s) {
  let sum = 0, mag = 1
  for(let i = s.length - 1; i >= 0; i--){
    let digit = s.charCodeAt(i) - 'A'.charCodeAt(0) + 1
    sum += mag * digit
    mag *= 26
  }
  return sum
};

Time complexity: O(n)
- where n is the number of chars in s
Space complexity: O(1)