例如，
1 -> A
2 -> B
3 -> C
...
26 -> Z
27 -> AA
28 -> AB
...
示例 1:
输入: 1
输出: "A"
示例 2:
输入: 28
输出: "AB"
示例 3:
输入: 701
输出: "ZY"
public static String convertToTitle(int n) {
StringBuilder sb = new StringBuilder();
while(n>26) {
int tmp = n % 26;
n /= 26;
if(tmp == 0) {
tmp = 26;
n = n - 1;
}
sb.insert(0, (char)(tmp+64));
}
sb.insert(0, (char)(n+64));
return sb.toString();
}