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[LeetCode 171] Excel Sheet Column Number

Problem

Given a string columnTitle that represents the 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: 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"].

Thoughts

  • Find char code
  • 26 base number

TypeScript

function titleToNumber(columnTitle: string): number {
    let res = 0;
    let power = 0;
    const charCodeA: number = 'A'.charCodeAt(0)
    
    for(let i = columnTitle.length - 1; i >=0; i--){
        res += (26**power * (columnTitle.charCodeAt(i) - charCodeA + 1))
        power++;
    }
    
    return res;
};

Reference