Lintcode 49. Sort Letters by Case

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

Example

Example 1:
 Input:  "abAcD"
 Output:  "acbAD"

Example 2:
 Input: "ABC"
 Output:  "ABC"
 

Challenge

Do it in one-pass and in-place.

Notice

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

Code (Java):

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public class Solution {     /*      * @param chars: The letter array you should sort by Case      * @return: nothing      */     public void sortLetters(char[] chars) {         if (chars == null || chars.length < 2) {             return;         }                   int start = 0;         int end = chars.length - 1;                   while (start <= end) {             while (start <= end && Character.isLowerCase(chars[start])) {                 start++;             }                           while (start <= end && Character.isUpperCase(chars[end])) {                 end--;             }                           if (start <= end) {                 swap(chars, start, end);                 start++;                 end--;             }         }     }           private void swap(char[] chars, int i, int j) {         char temp = chars[i];         chars[i] = chars[j];         chars[j] = temp;     } }