What is the main concept behind solving the 'Excel Sheet Column Number' problem?

The problem is solved using a base-26 number system, where each letter corresponds to a value ('A' = 1, 'B' = 2, etc.), and the result is computed iteratively by adjusting for place value.

How do I handle the edge case of the shortest column title, 'A'?

Simply return 1 since 'A' corresponds to the first column in Excel.

Can this solution be optimized for very large column titles?

The solution already operates in O(n) time, where n is the length of the string. There is no need for further optimization unless the constraints change significantly.

What are the constraints for this problem?

The column title can be between 1 and 7 characters long, consisting only of uppercase letters, and the title is in the range from 'A' to 'FXSHRXW'.

Why is the time complexity O(n) for this problem?

The time complexity is O(n) because we process each character of the input string exactly once, performing a constant amount of work for each character.

#171

Easy

auto_awesome数学·string

LeetCode 题解工作台

Excel 表列序号

给你一个字符串 columnTitle ，表示 Excel 表格中的列名称。返回该列名称对应的列序号。例如： A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... 示例 1: 输入: columnTitle = "A" 输出: 1 示例 …

数学字符串

题目描述

给你一个字符串 columnTitle ，表示 Excel 表格中的列名称。返回 该列名称对应的列序号 。

例如：

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28 
...

示例 1:

输入: columnTitle = "A"
输出: 1

示例 2:

输入: columnTitle = "AB"
输出: 28

示例 3:

输入: columnTitle = "ZY"
输出: 701

提示：

1 <= columnTitle.length <= 7
columnTitle 仅由大写英文组成
columnTitle 在范围 ["A", "FXSHRXW"] 内

lightbulb

解题思路

方法一：进制转换

Excel 表格中的列名称是一种 26 进制的表示方法。例如，"AB" 表示的列序号是 $1 \times 26 + 2 = 28$ 。

因此，我们可以遍历字符串 columnTitle，将每个字符转换为对应的数值，然后计算结果即可。

时间复杂度 $O(n)$ ，其中 $n$ 是字符串 columnTitle 的长度。空间复杂度 $O(1)$ 。

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class Solution:
    def titleToNumber(self, columnTitle: str) -> int:
        ans = 0
        for c in map(ord, columnTitle):
            ans = ans * 26 + c - ord("A") + 1
        return ans

speed

复杂度分析

指标	值
时间	Depends on the final approach
空间	Depends on the final approach

psychology

面试官常问的追问

外企场景

question_mark
Look for a candidate who uses a mathematical approach to solve the problem, rather than brute-forcing through all possible values.
question_mark
The ability to handle the base-26 conversion correctly is key to solving the problem efficiently.
question_mark
Check if the candidate can identify and explain potential edge cases like the shortest and longest column titles.

warning

常见陷阱

外企场景

error
Candidates may fail to account for the place value when calculating the column number, leading to incorrect results.
error
Some may treat the problem like a simple string manipulation problem rather than recognizing the base-26 nature of the column title.
error
Misunderstanding the range of column titles, especially with long titles like 'FXSHRXW', could lead to performance issues.

swap_horiz

进阶变体

外企场景

arrow_right_alt
What happens if the column title is in lowercase? (Adjust for case sensitivity.)
arrow_right_alt
Can this approach be optimized for large strings if we have a maximum length greater than 7 characters?
arrow_right_alt
How would the problem change if the column titles were in a different base, like base-10?

help

常见问题

外企场景

继续练习

#168 Excel 表列名称 #166 分数到小数 #224 基本计算器