Excel Sheet Column Number

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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, ..., Z → 26, AA → 27, AB → 28, ..., ZY → 701.

Example 1
Input: columnTitle = "A"
Output: 1
Example 2
Input: columnTitle = "AB"
Output: 28
Explanation: A=1, B=2. AB = 1*26 + 2 = 28.
Example 3
Input: columnTitle = "ZY"
Output: 701

Solution Approach

This is essentially a base-26 to decimal conversion. Process characters left to right, accumulating the result by multiplying by 26 at each step and adding the value of the current character (A=1, B=2, ..., Z=26).

  • Initialize result = 0.
  • For each character c: result = result * 26 + (c - 'A' + 1).
  • Return result.
Java
class Solution {
    public int titleToNumber(String columnTitle) {
        int result = 0;
        for (char c : columnTitle.toCharArray()) {
            result = result * 26 + (c - 'A' + 1);
        }
        return result;
    }
}
Complexity Analysis:

Time complexity: O(n) where n is the length of the column title string.
Space complexity: O(1). Only a result variable is used.