一、数字转字母
//数字转字母 1-26 : A-Z
private String numberToLetter(int num) {
if (num <= 0) {
return null;
}
String letter = "";
num--;
do {
if (letter.length() > 0) {
num--;
}
letter = ((char) (num % 26 + (int) 'A')) + letter;
num = (int) ((num - num % 26) / 26);
} while (num > 0);
return letter;
}//数字转字母 1-26 : A-Z
private String num