Strings

Strings

using System;
using System.Text;

namespace Strings
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("itoa for {0} is {1}", -234, itoa(-234));
            Console.WriteLine("itoa for {0} is {1}", 1.1111, itoa(1.1111));
            Console.WriteLine("atoi for {0} is {1}", "-234", atoi("-234"));
            Console.WriteLine("atoi for {0} is {1}", "0", atoi("0"));
            Console.WriteLine("atod for {0} is {1}", "236.45", atod("236.45"));
            Console.WriteLine("atod for {0} is {1}", "236", atod("236"));
            
            Console.WriteLine("Is {0} a palindrome?: {1}", "abba", isPalindrome("abba"));
            Console.WriteLine("Is {0} a palindrome?: {1}", "abkeba", isPalindrome("abkeba"));
            
            Console.WriteLine("Does {0} have unique characters?: {1}", "abccdef", hasUniqueCharacters("abccdef"));
            Console.WriteLine("Does {0} have unique characters?: {1}", "×", hasUniqueCharacters("×"));
        }
        
        static string reverse(string s) {
            StringBuilder sb = new StringBuilder(s);
            
            for(int i = 0; i < sb.Length / 2; i++) {
                char temp = sb[i];
                sb[i] = sb[sb.Length - 1 - i];
                sb[sb.Length - 1 - i] = temp;
            }
            
            return sb.ToString();
        }
        
        static string itoa(int num) {
            bool isNegative = false;
            
            if (num == 0) {
                return "0";
            }
            
            if (num < 0) {
                isNegative = true;
                num *= -1;
            }
            
            StringBuilder sb = new StringBuilder("");
            
            while (num > 0) {
                char digit = (char)((num % 10) + '0');
                sb.Append(digit);
                num = num / 10;
            }
            
            if (isNegative) {
                sb.Append('-');
            }
            
            return reverse(sb.ToString());
            
        }
        
        static string itoa(double num) {
            int integerVal = (int)num;
            
            int numOfDecimalPoints = 0;
            
            double difference = integerVal * 0.0001;
            
            while (Math.Abs((double)integerVal - num) >= difference) {
                numOfDecimalPoints++;
                num *= 10;
                integerVal = (int)(num);
                Console.WriteLine("Int value is " + integerVal);
                Console.WriteLine("Double value is " + num);
            }
            
            StringBuilder sb = new StringBuilder(itoa(integerVal));
            sb.Insert(sb.Length - numOfDecimalPoints, '.');
            
            return sb.ToString();
        }
        
        static int atoi(string s) {
            if (String.IsNullOrEmpty(s)) {
                throw new Exception("Invalid Input");
            }
            
            int current = 0;
            
            bool isNegative = false;
            
            if (s[0] == '-') {
                current = 1;
                isNegative = true;
            }
            
            int result = 0;
            while (current < s.Length) {
                
                if (!Char.IsDigit(s[current])) {
                    throw new Exception("Invalid input");
                }
                result = (result * 10) + (int)(s[current] - '0');
                current++;
            }
            
            if (isNegative) {
                result *= -1;
            }
            
            return result;
        }
        
        static double atod(string s) {
            if (String.IsNullOrEmpty(s)) {
                throw new Exception("Invalid Input");
            }
            
            if (s.Contains(".")) {
                string[] inputs = s.Split('.');
                if (inputs.Length > 2) {
                    throw new Exception("Invalid input");
                }
                
                int beforeDecimal = atoi(inputs[0]);
                int afterDecimal = atoi(inputs[1]);
                
                return (beforeDecimal + (afterDecimal / Math.Pow(10, inputs[1].Length)));
            } else {
                return atoi(s);
            }
        }
        
        static bool isPalindrome(string s) {
            if (String.IsNullOrEmpty(s) || String.IsNullOrWhiteSpace(s)) {
                return false;
            }
            
            for (int i = 0; i <= s.Length / 2; i++) {
                if (s[i] != s[s.Length - 1 - i]) {
                    return false;
                }
            }
            
            return true;
        }
        
        // assuming input only has ASCII characters
        static bool hasUniqueCharacters(string s) {
            bool[] charMap = new bool[256];
            
            foreach (char ch in s) {
                if (charMap[ch]) {
                    return false;
                } else {
                    charMap[ch] = true;
                }
            }
            
            return true;
        }
    }
}