LeetCode 168. Excel Sheet Column Title

原题链接在这里: https://leetcode.com/problems/excel-sheet-column-title/

题目：

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

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

题解：

不是从0开始算，这里是从1算起. 算之前先对n进行n-1处理再取余数。

Time Complexity: O(res.length()).

Space: O(res.length()).

AC Java:

class Solution {
    public String convertToTitle(int n) {
        if(n <= 0){
            throw new IllegalArgumentException("Invalid input integer.");
        }
        
        StringBuilder sb = new StringBuilder();
        while(n != 0){
            sb.insert(0, (char)('A'+(n-1)%26));
            n = (n-1)/26;
        }
        
        return sb.toString();
    }
}

recursion写法.

Time Complexity: O(res.length()). Space: O(res.length()).

AC Java:

class Solution {
    public String convertToTitle(int n) {
        if(n == 0){
            return "";
        }
        
        n = n-1;
        return convertToTitle(n/26) + (char)('A'+ (n%26));
    }
}

类似Excel Sheet Column Number.