Excel Sheet Column Number
easyTime: O(n)Space: O(1)
Signals to notice
Excel column letters to numberbase-26 with A=1left-to-right accumulation
Brute force first
Not applicable — direct computation.
The key insight
result = result × 26 + (char - 'A' + 1). Process left to right. O(n).
What must stay true
It's base-26 but 1-indexed: A=1, B=2, ..., Z=26. Each position multiplied by 26^distance from right.
Easy way to go wrong
Using A=0 — Excel columns are 1-indexed.