Lintcode: Sort Letters by Case

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.

 1 public class Solution {

 2     /** 

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

 4      *@return: void

 5      */

 6     public void sortLetters(char[] chars) {

 7         //write your code here

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

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

10         while (true) {

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

12                 l++;

13             }

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

15                 r--;

16             }

17             if (l == r) break;

18             swap(chars, l, r);

19         }

20     }

21     

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

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

24         else return false;

25     }

26     

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

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

29         else return false;

30     }

31     

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

33         char temp = chars[l];

34         chars[l] = chars[r];

35         chars[r] = temp;

36     }

37 }