O(n) time and O(1) space

Author: 149ps

30 Days August Challange/Week 2/4. Excel Sheet Column Number/solution.py

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+"""
+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".
+"""
+class Solution:
+    def titleToNumber(self, s: str) -> int:
+        result = 0
+        for i,char in enumerate(s[::-1]):
+            result += (ord(char) - ord('A') + 1 ) * (26**i)
+        return result