[LeetCode] Excel Sheet Column Title

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

Credits:

Special thanks to @ifanchu for adding this problem and creating all test cases.

public class Solution {
public String convertToTitle(int n) {
ArrayList<Character> res = new ArrayList<Character>();
while(n > 26) {
int tmp = n % 26;

if (tmp == 0) res.add(0, 'Z');
else res.add(0, (char) ('A' + tmp-1));
int m = n;
n /= 26;
if ( n*26 - m == 0) n -= 1;
}

res.add(0,(char)('A' + n-1));

String ress = new String();
for (int i = 0; i < res.size(); i++) {
ress += res.get(i);
}
return ress;
}
}