Given a string which contains only letters. Sort it by lower case first and upper case second.

Note

It's not necessary to keep the original order of lower-case letters and upper case letters.

Example

For "abAcD", a reasonable answer is "acbAD"

Challenge

Do it in one-pass and in-place.

 public class Solution {

     /**

      *@param chars: The letter array you should sort by Case

      *@return: void

      */

     public void sortLetters(char[] chars) {

         //write your code here

         if (chars==null || chars.length==0) return;

         int l=0, r=chars.length-1;

         while (true) {

             while (l<r && isLower(chars, l)) {

                 l++;

             }

             while (l<r && isUpper(chars, r)) {

                 r--;

             }

             if (l == r) break;

             swap(chars, l, r);

         }

     }

     public boolean isLower(char[] chars, int index) {

         if (chars[index]>='a' && chars[index]<='z') return true;

         else return false;

     }

     public boolean isUpper(char[] chars, int index) {

         if (chars[index]>='A' && chars[index]<='Z') return true;

         else return false;

     }

     public void swap(char[] chars, int l, int r) {

         char temp = chars[l];

         chars[l] = chars[r];

         chars[r] = temp;

     }

 }