README_EN.md

comments	difficulty	edit_url	tags
true	Easy	https://github.com/doocs/leetcode/edit/main/solution/0100-0199/0171.Excel%20Sheet%20Column%20Number/README_EN.md	Math String

171. Excel Sheet Column Number

中文文档

Description

Given a string columnTitle that represents the column title as appears 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: columnTitle = "A"
Output: 1

Example 2:

Input: columnTitle = "AB"
Output: 28

Example 3:

Input: columnTitle = "ZY"
Output: 701

 

Constraints:

• 1 <= columnTitle.length <= 7
• columnTitle consists only of uppercase English letters.
• columnTitle is in the range ["A", "FXSHRXW"].

Solutions

Solution 1: Base Conversion

The column name in Excel is a representation in base 26. For example, "AB" represents the column number $1 \times 26 + 2 = 28$.

Therefore, we can iterate through the string columnTitle, convert each character to its corresponding value, and then calculate the result.

The time complexity is $O(n)$, where $n$ is the length of the string columnTitle. The space complexity is $O(1)$.

Python3

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

Java

class Solution {
    public int titleToNumber(String columnTitle) {
        int ans = 0;
        for (int i = 0; i < columnTitle.length(); ++i) {
            ans = ans * 26 + (columnTitle.charAt(i) - 'A' + 1);
        }
        return ans;
    }
}

C++

class Solution {
public:
    int titleToNumber(string columnTitle) {
        int ans = 0;
        for (char& c : columnTitle) {
            ans = ans * 26 + (c - 'A' + 1);
        }
        return ans;
    }
};

Go

func titleToNumber(columnTitle string) (ans int) {
	for _, c := range columnTitle {
		ans = ans*26 + int(c-'A'+1)
	}
	return
}

TypeScript

function titleToNumber(columnTitle: string): number {
    let ans: number = 0;
    for (const c of columnTitle) {
        ans = ans * 26 + (c.charCodeAt(0) - 'A'.charCodeAt(0) + 1);
    }
    return ans;
}

C#

public class Solution {
    public int TitleToNumber(string columnTitle) {
        int ans = 0;
        foreach (char c in columnTitle) {
            ans = ans * 26 + c - 'A' + 1;
        }
        return ans;
    }
}