65. Valid Number

65. Valid Number

题目

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. 

解析

    //链接：https://www.nowcoder.com/questionTerminal/608d810765a34df2a0d47645626dd2d3
	class Solution {
	public:
		bool isNumber(const char *s)
		{
			string str(s);
			int index = str.find_first_not_of(' ');
			if (str[index] == '+' || str[index] == '-') //正负号
				index++;
			int points = 0, numbers = 0;
			for (; str[index] >= '0' && str[index] <= '9' || str[index] == '.'; index++)
				s[index] == '.' ? ++points : ++numbers;
			if (points > 1 || numbers < 1)
				return false;

			if (str[index] == 'e' || str[index] == 'E')
			{
				index++;
				if (str[index] == '+' || str[index] == '-') // E后面也有正负号
					index++;
				int afterE = 0;
				for (; str[index] >= '0' && str[index] <= '9'; index++)
					afterE++;
				if (afterE < 1)
					return false;
			}
			for (; str[index] == ' '; index++){}
			return str[index] == '\0';
		}
	};

题目来源

• 65. Valid Number