ValidNumber.cs

// Source : https://leetcode.com/problems/valid-number/ 
// Author : codeyu 
// Date : Sunday, December 11, 2016 4:12:06 PM 

/**********************************************************************************
*
* Validate if a given string is numeric.
* 
* 
* Some examples:
* "0" => true
* "   0.1  " => true
* "abc" => false
* "1 a" => false
* "2e10" => true
* 
* 
* Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.
* 
* 
* 
* Update (2015-02-10):
* The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button  to reset your code definition.
* 
*
**********************************************************************************/

using System;
using System.Collections.Generic;
using Algorithms.Utils;
namespace Algorithms
{
    public class Solution065
    {
        public static bool IsNumber(string s)
        {
            if(s==null)  
                return false;  
            s = s.Trim();  
            if(s.Length==0)  
                return false;  
            bool dotFlag = false;  
            bool eFlag = false;  
            for(int i=0;i<s.Length;i++)  
            {  
                switch(s[i])  
                {  
                    case '.':  
                        if(dotFlag || eFlag   
                        || ((i==0||!(s[i-1]>='0'&&s[i-1]<='9'))   
                            && (i==s.Length-1||!(s[i+1]>='0'&&s[i+1]<='9'))))  
                            return false;  
                        dotFlag = true;  
                        break;  
                    case '+':  
                    case '-':  
                        if((i>0 && (s[i-1]!='e' && s[i-1]!='E'))  
                        || (i==s.Length-1 || !(s[i+1]>='0'&&s[i+1]<='9'||s[i+1]=='.')))  
                            return false;  
                        break;  
                    case 'e':  
                    case 'E':  
                        if(eFlag || i==s.Length-1 || i==0)  
                            return false;  
                        eFlag = true;  
                        break;  
                    case '0':  
                    case '1':  
                    case '2':  
                    case '3':  
                    case '4':  
                    case '5':  
                    case '6':  
                    case '7':  
                    case '8':  
                    case '9':  
                        break;  
                    default:  
                        return false;  
                }  
            }  
            return true; 

        }
    }
}