168. Excel Sheet Column Title 

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
class Solution {
    public String convertToTitle(int columnNumber) {
        // 1 -> A
        // 26 -> Z

        // 28 -> AB
        // 28 =  1 * 26 + 2

        // 27 -> AA
        // 27 =  1 * 26 + 1

        // 52 -> AZ
        // 52 =  1 * 26 + 26

        // range: [1, 26], 注意并非从 0 开始

        StringBuilder sb = new StringBuilder();
        while (columnNumber >= 1) {
            int mod = (columnNumber - 1) % 26; // [0, 25]
            sb.append((char)('A' + mod));
            columnNumber = (columnNumber - 1) / 26;
        }
        return sb.reverse().toString();
    }
}

References

168. Excel Sheet Column Title