有效数字

给定一个字符串，验证其是否为数字。

样例

"0" => true

" 0.1 " => true

"abc" => false

"1 a" => false

"2e10" => true

class Solution {
public:
    /**
     * @param s the string that represents a number
     * @return whether the string is a valid number
     */
    bool isNumber(string& s) {
        // Write your code here
        int n = s.length();
	    int begin = 0;
	    int end = n-1;
	    while (s[begin] == ' ')
	    {
		    begin++;
	    }
	    while (s[end] == ' ')
	    {
		    end--;
	    }
        if (begin > end)
        {
            return false;
        }
	    bool dotFound = false;
	    bool eFound = false;
	    bool numFound = false;
	    for (int i = begin; i <= end; i++)
	    {
		    if (s[i] <= '9' && s[i] >= '0')
		    {
		        numFound = true;
			    continue;
		    }
		    else if (s[i] == '.')
		    {
		        if (i == end)
		        {
		            return false;
		        }
			    else if (dotFound || eFound)
			    {
				    return false;
			    }
			    else
			    {
				    dotFound = true;
				    continue;
			    }
		    }
		    else if (s[i] == 'e')
		    {
		        if (!numFound || i == end)
		        {
		            return false;
		        }
			    else if (dotFound || eFound)
			    {
				    return false;
			    }
			    else
			    {
				    eFound = true;
				    continue;
			    }
		    }
		    else
		    {
			    return false;
		    }
	    }

	    return true;
    }
};