问在Java中生成字母序列

EN

static String str(int i) {
    return i < 0 ? "" : str((i / 26) - 1) + (char)(65 + i % 26);
}

public static void main(String[] args) {
    for (int i = 0; i < 27*27; ++i) {
        System.out.println(i + " -> " + str(i));
    }
}

0 -> A
1 -> B
2 -> C
[...]
24 -> Y
25 -> Z
26 -> AA
27 -> AB
[...]
700 -> ZY
701 -> ZZ
702 -> AAA
703 -> AAB
[...]
727 -> AAZ
728 -> ABA

import static java.lang.Math.*;

private static String getString(int n) {
    char[] buf = new char[(int) floor(log(25 * (n + 1)) / log(26))];
    for (int i = buf.length - 1; i >= 0; i--) {
        n--;
        buf[i] = (char) ('A' + n % 26);
        n /= 26;
    }
    return new String(buf);
}

public class SeqGen {
    public static void main(String[] args) {
        //This is the configurable param
        int seqWidth = 3;

        Double charSetSize = 26d;

        // The size of the array will be 26 ^ seqWidth. ie: if 2 chars wide, 26
        // * 26. 3 chars, 26 * 26 * 26
        Double total = Math.pow(charSetSize, (new Integer(seqWidth)).doubleValue());

        StringBuilder[] sbArr = new StringBuilder[total.intValue()];
        // Initializing the Array
        for(int j = 0; j <total; j++){
            sbArr[j] = new StringBuilder();
        }

        char ch = 'A';
        // Iterating over the entire length for the 'char width' number of times.
        // TODO: Can these iterations be reduced?
        for(int k = seqWidth; k >0; k--){
            // Iterating and adding each char to the entire array.        
            for(int l = 1; l <=total; l++){
                sbArr[l-1].append(ch);
                if((l % (Math.pow(charSetSize, k-1d))) == 0){
                    ch++;
                    if(ch > 'Z'){
                        ch = 'A';
                    }
                }
            }
        }

        //Use the stringbuilder array.
        for (StringBuilder builder : sbArr) {
            System.out.println(builder.toString());
        }
    }
}