Excel Sheet Column Number

You can convert the Excel column title to its corresponding column number by treating the string as a base-26 number. Here’s a simple explanation and the corresponding code:

  1. Initialization: Start by initializing a variable to store the column number.
  2. Iterate through the string: For each character in the columnTitle string, multiply the current column number by 26 (since there are 26 letters in the alphabet) and add the numeric value of the current character (subtract ‘A’ and add 1).
  3. Return: Return the calculated column number.

Here’s the code:

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class Solution:
    def titleToNumber(self, columnTitle: str) -> int:
        columnNumber = 0
        for char in columnTitle:
            columnNumber = columnNumber * 26 + (ord(char) - ord('A') + 1)
        return columnNumber

Explanation:

  • For every character in the string, you’re multiplying the current value by 26 (like shifting a digit in base-26) and adding the value of the current character.
  • ord(char) - ord('A') + 1 computes the numeric value of the current character (A = 1, B = 2, etc.).

This code will convert the given column title into the corresponding column number, meeting the problem’s constraints.

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class Solution:
    def titleToNumber(self, columnTitle: str) -> int:
        ans, pos = 0, 0
        for letter in reversed(columnTitle):
            digit = ord(letter)-64
            ans += digit * 26**pos
            pos += 1

        return ans

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class Solution:
    def titleToNumber(self, columnTitle: str) -> int:
        abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        ans = 0

        for i in range(len(columnTitle)):
            ans = ans * 26 + abc.index(columnTitle[i]) + 1

        return ans

Problem Classification

The problem involves converting a string (Excel column title) into a number (corresponding column number).

  1. String Manipulation: The problem requires the manipulation and processing of strings (i.e., converting string representation of Excel columns into integer column number).

  2. Number Systems Conversion: This is because the problem is essentially converting a base-26 number (Excel column title, where A=1, B=2, …, Z=26, AA=27, etc.) into a base-10 number. Hence, the problem involves concepts related to number system conversion.

  3. Mathematical Computation: The computation process involves operations like exponentiation and multiplication, which fall under mathematical computation.

The actual solution could involve additional programming concepts such as loops, arrays, or recursion, etc. depending on the approach taken.

Language Agnostic Coding Drills

  1. String Manipulation: Understand how to iterate through characters in a string.

  2. Mathematical Operations: Basic mathematical operations are used here, like addition and multiplication.

  3. Power of a Number: Familiarize yourself with how to calculate the power of a number, which in this case is used to implement the base-26 calculation.

  4. Character to ASCII Conversion: Learn how to convert characters to their corresponding ASCII values. This is used to convert alphabets to corresponding numeric values.

  5. Reversed Iteration: Understand how to iterate through a sequence in reversed order. This is essential because the calculation is based on the position of characters, starting from the end of the string.

  6. Accumulative Addition: Learn how to continuously add values to a variable. This is used to calculate the final result.

In terms of the problem-solving approach:

  • The problem statement asks to convert a column title (as it appears in an Excel sheet) to its corresponding column number.

  • Excel column titles are in base-26 numeral system represented by alphabets (A-Z). A is 1, B is 2, …, Z is 26, AA is 27, and so on.

  • The problem-solving approach involves processing the column title string from right to left (or least significant character to most significant).

  • For each character, we convert it to its corresponding numeric value (1-26), then multiply it by 26 to the power of its position. The position starts from 0 for the rightmost character.

  • We then add this value to the running total (which starts at 0).

  • The final result after processing all the characters in the string is the column number corresponding to the given column title.

Targeted Drills in Python

Drill 1 - String Manipulation:

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# Create a string
s = "Hello, world!"

# Iterate through each character in the string
for char in s:
    print(char)

Drill 2 - Mathematical Operations:

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# Perform basic mathematical operations
a = 10
b = 2
print(a + b)
print(a * b)

Drill 3 - Power of a Number:

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# Calculate the power of a number
base = 2
exponent = 3
result = base ** exponent
print(result)

Drill 4 - Character to ASCII Conversion:

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# Convert a character to its ASCII value
char = 'A'
ascii_value = ord(char)
print(ascii_value)

Drill 5 - Reversed Iteration:

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# Iterate through a sequence in reversed order
sequence = [1, 2, 3, 4, 5]
for i in reversed(sequence):
    print(i)

Drill 6 - Accumulative Addition:

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# Continuously add values to a variable
total = 0
for i in range(10):
    total += i
print(total)

Problem-Specific Drill: Converting Excel Column Titles to Numbers:

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# Convert an Excel column title to its corresponding column number
title = "AB"
result = 0
for i, char in enumerate(reversed(title)):
    digit = ord(char) - 64
    result += digit * (26 ** i)
print(result)

Each of these drills represents a piece of the final solution. Practicing these drills will help you become familiar with the concepts and techniques needed to solve the problem, and the final drill demonstrates how to integrate these skills to solve the problem at hand.