Excel Sheet Column Title

Problem

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

Solution

My original solution using StringBuilder

public class Solution {
    public String convertToTitle(int n) {
        StringBuilder sb = new StringBuilder();
        while (n > 26) {
            n--;
            char val = (char) (n % 26 + 'A'); // 1 = 'A', so we decrement n by 1 above 
            sb.append(val);
            n /= 26;
        }
        sb.append((char) (n - 1 + 'A'));
        return sb.reverse().toString();
    }
}

One line recursive solution

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

Analysis

This is a typical problem about decimal conversion
The first solution is to construct digit from the ending position
The second solution is to construct digit from the beginning position