65. Valid Number

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65. Valid Number

Description

Given a string s, return whether s is a valid number.

For example, all the following are valid numbers: "2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789", while the following are not valid numbers: "abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53".

Formally, avalid number is defined using one of the following definitions:

  • An integer number followed by an optional exponent .
  • A decimal number followed by an optional exponent .

An integer number is defined with an optional sign '-' or '+' followed by digits .

A decimal number is defined with an optional sign '-' or '+' followed by one of the following definitions:

  • Digits followed by a dot '.'.
  • Digits followed by a dot '.' followed by digits .
  • A dot '.' followed by digits .

An exponent is defined with an exponent notation 'e' or 'E' followed by an integer number .

The digits are defined as one or more digits.

Example 1:

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Input: s = "0"

Output: true

Example 2:

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Input: s = "e"

Output: false

Example 3:

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Input: s = "."

Output: false

Constraints:

  • 1 <= s.length <= 20
  • s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    bool isNumber(string s) {
        int idx_e = -1;
        for (int i = 0; i < s.size(); i++) {
            if (s[i] == 'e' || s[i] == 'E') {
                if (idx_e == -1) {
                    idx_e = i;
                } else {
                    return false;
                }
            }
        }
        if (idx_e == -1) {
            return checkNum(s, 0, s.size() - 1, false);
        } else {
            return checkNum(s, 0, idx_e - 1, false) && checkNum(s, idx_e + 1, s.size() - 1, true);
        }
    }

    bool checkNum(string& s, int start, int end, bool mustInt) {
        if (start > end) {
            return false;
        }
        if (s[start] == '+' || s[start] == '-') {
            start++;
        }
        bool decimal = false, isNum = false;
        for (int i = start; i <= end; i++) {
            if (isdigit(s[i])) {
                isNum = true;
                continue;
            } else if (s[i] == '.') {
                if (decimal || mustInt) {
                    return false;
                }
                decimal = true;
            } else {
                return false;
            }
        }
        return isNum;
    }
};