Leetcode 125 - valid palindrome - study code - https://github.com/jianminchen/leetcode-cpp/blob/master/src/ValidPalindrome.cpp, use continue keyword

Leetcode125_validPalindrome_PB.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Leetcode125_IsPalindrome
{
    class Program
    {
        /*
         *  Leetcode 125: is palindrome 
         *  
         *  blog to read: 
         *  http://blog.csdn.net/nomasp/article/details/50623165
         */
        static void Main(string[] args)
        {
            bool test = isPalindrome("Aa");
            bool test2 = isPalindrome("Ab%Ba");
            bool test3 = isPalindrome("B%1*1b");
        }

        /*
         * Function design:
         * 
         * study the code:
         * https://github.com/jianminchen/leetcode-cpp/blob/master/src/ValidPalindrome.cpp
         * 
         * Time complexity: 
         * O(N)
         * 
         * use continue keyword to make the code more clear, based on practice #9 
         * 
         */
        public static bool isPalindrome(string s)
        {
            if (s == null || s.Length == 0)
                return true;

            int left = 0;
            int right = s.Length - 1;

            // Enforce the rule that one iteration in while loop only work on one of if case, therefore, 
            // more easy to follow. 
            // continue - line 60, line 66 
            // - also - remove 4th if 
            while (left < right)
            {
                char c1 = s[left];
                char c2 = s[right];

                bool[] arr = new bool[2] { isAlnum(c1), isAlnum(c2) };

                bool isComparable = arr[0] && arr[1];
                bool isSame = toUpper(c1) == toUpper(c2);

                if (!isComparable && !arr[0])
                {
                    left++;
                    continue; 
                }

                if (!isComparable && !arr[1])
                {
                    right--;
                    continue; 
                }

                if (isComparable && !isSame)
                    return false;

                //if (isComparable && isSame)
                //{
                    left++;
                    right--;
                //}
            }

            return true; 
        }

        /*
         * a-z
         * A-Z
         * 0-9
         */
        private static bool isAlnum(char c)
        {
            const int SIZE = 26;
            int[] arr = new int[] { c - 'a', c - 'A', c - '0' };

            // is A-Z or a-z or 0 -9
            if ((arr[0] >= 0 && arr[0] <  SIZE) ||
                (arr[1] >= 0 && arr[1] <  SIZE) ||
                (arr[2] >= 0 && arr[2] <= 9))
                return true;

            return false;
        }

        /*
         * 
         */
        private static char toUpper(char c)
        {
            int no = c - 'a';

            if (no >= 0 && no < 26)
                return (char)('A' + no);
            else
                return c;
        }        
    }
}