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