lintcode 中等题:sort letters by case字符大小写排序

public class Solution {
    /** 
     *@param chars: The letter array you should sort by Case
     *@return: void
     */
    public void sortLetters(char[] chars) {
        //write your code here
        int len = chars.length;
        if(len ==0 || chars==null){
            
        }else{
            int i=0;
            int j=len-1;
            while(i<=j){
                while(i<=j && isLowerCase(chars[i])) i++;
                while(i<=j && isUpperCase(chars[j])) j--;
                if(i<=j){
                    char ch = chars[i];
                    chars[i] = chars[j];
                    chars[j] = ch;
                }
            }
        }
        
    }
    public boolean isLowerCase(char ch){
        if(ch>=‘a‘ && ch<=‘z‘)
            return true;
        return false;
    }
    public boolean isUpperCase(char ch){
        if(ch>=‘A‘ && ch<=‘Z‘)
            return true;
        return false;
    }
    
}