LeetCode 168. Excel Sheet Column Title

public class Solution {
    
    char[] letter;
    
    public String convertToTitle(int n) {
        init();
        StringBuilder sb = new StringBuilder();
        
        n--;
        if( n == 0) return "A";
        
        while(n >= 0) {
            sb.insert(0, letter[n%26]);
            
            if(n == 0) break;
            n /= 26;
            n--;
        }
        return sb.toString();
    }
    
    public void init() {
        letter = new char[26];
        for(int i = 0; i < 26; i++)
            letter[i] = (char)(‘A‘+i);
    }
    
}