Valid Number(Hard)

题目描述

Validate if a given string is numeric.

Example

"0" => true  
" 0.1 " => true  
"abc" => false  
"1 a" => false  
"2e10" => true

题目链接

解题思路

给几组比较容易漏掉的例子：

• "e" => false
• "." => false
• "1 " => false
• "+.8" => true
• " " => false
• "54 aa" => false

参考程序

class Solution {
public:
    /**
     * @param s the string that represents a number
     * @return whether the string is a valid number
     */
    bool isNumber(string& t) {
        // Write your code her
        string s = "";
        int i = 0, m = t.length();
        while (i < m && t[i] == ' ') ++ i;
        if (i >= m) return false;
        while (i < m && t[i] != ' ') s.push_back(t[i ++]);
        while (i < m && t[i] == ' ') ++ i;
        if (i < m) return false;

        for (char ch: s) if (ch != '+' && ch != '-' && ch != '.' && ch != 'e' && !isdigit(ch)) return false;
        int cnt_e = 0, cnt_dot = 0;
        for (char ch: s) {
            if (ch == 'e') ++ cnt_e;
            else if (ch == '.') {
                ++ cnt_dot;
            }
        }
        if (cnt_e > 1 || cnt_dot > 1) return false;
        int n = s.length();
        bool has_e = false;
        for (int i = 0; i < n; ++ i) {

            if (s[i] == 'e') {
                if (i == 0) return false;
                else if (i == 1 && s[i - 1] == '.') return false;
                has_e = true;
            } else if (s[i] == '.' ) {
                if (has_e) return false;
                bool flag = false;
                if (i > 0 && isdigit(s[i - 1])) flag = true;
                if (i < n - 1 && isdigit(s[i + 1])) flag = true;
                if (flag == false) return false;
            }
        }
        return true;
    }
};