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Excel Sheet Column Number – Solution & Complexity

Interview solutions
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Excel Sheet Column Number

1. Understand the Pattern

  • The title behaves like a base-26 number, but the digits run 1..26, not 0..25.
  • A contributes 1, Z contributes 26.
  • Reading left to right, each new letter shifts the running total up by a factor of 26.

2. Map a Letter to Its Value

  • Subtract the code point of A and add 1.
  • So A -> 1, B -> 2, ..., Z -> 26.
  • This is the per-digit value for the base-26 sum.
def letter_value(ch):
    return ord(ch) - ord('A') + 1

3. Accumulate Left to Right

  • Start the result at 0.
  • For each letter, multiply the result by 26 and add the letter's value.
  • After the last letter the result is the column number.
def title_to_number(column_title):
    result = 0
    for ch in column_title:
        result = result * 26 + (ord(ch) - ord('A') + 1)
    return result

4. Final Solution and Complexity

  • Each character is visited once.
  • Time complexity is O(L) for a title of length L.
  • Space complexity is O(1).
def title_to_number(column_title: str) -> int:
    result = 0
    for ch in column_title:
        result = result * 26 + (ord(ch) - ord('A') + 1)
    return result

FAQ

See also

Practice Excel Sheet Column Number online (run code in the browser)FizzBuzz solution (easy)Roman to Integer solution (easy)Climbing Stairs solution (easy)Count Primes solution (medium)All coding interview problems
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