LeetCode解题报告（376) -- 65. Valid Number

Problem

A valid number can be split up into these components (in order):

1. A decimal number or an integer.
2. (Optional) An 'e' or 'E', followed by an integer.

A decimal number can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. One of the following formats:
   1. At least one digit, followed by a dot '.'.
   2. At least one digit, followed by a dot '.', followed by at least one digit.
   3. A dot '.', followed by at least one digit.

An integer can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. At least one digit.

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"].

Given a string s, return true if s is a valid number.

Example 1:

Input: s = "0"
Output: true

Example 2:

Input: s = "e"
Output: false

Example 3:

Input: s = "."
Output: false

Example 4:

Input: s = ".1"
Output: true

Constraints:

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

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Analysis

  这道题目要求我们验证给出的字符串是否一个合法的数字，这种题目考查的主要是各种case的判断。这道题目的情况实在是有点多，而且test case很复杂，直接参考LeetCode Valid Number。

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Solution

  无

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Code

class Solution {
public:
    bool isNumber(string s) {
        int len = s.size();
        int left = 0, right = len - 1;
        bool eExisted = false;
        bool dotExisted = false;
        bool digitExisited = false;
        // Delete spaces in the front and end of string
        while (s[left] == ' ') ++left;
        while (s[right] == ' ') --right;
        // If only have one char and not digit, return false
        if (left >= right && (s[left] < '0' || s[left] > '9')) return false;
        //Process the first char
        if (s[left] == '.') dotExisted = true;
        else if (s[left] >= '0' && s[left] <= '9') digitExisited = true;
        else if (s[left] != '+' && s[left] != '-') return false;
        // Process the middle chars
        for (int i = left + 1; i <= right - 1; ++i) {
            if (s[i] >= '0' && s[i] <= '9') digitExisited = true;
            else if (s[i] == 'e' || s[i] == 'E') { // e/E cannot follow +/-, must follow a digit
                if (!eExisted && s[i - 1] != '+' && s[i - 1] != '-' && digitExisited) eExisted = true;
                else return false;
            } else if (s[i] == '+' || s[i] == '-') { // +/- can only follow e/E
                if (s[i - 1] != 'e' && s[i - 1] != 'E') return false;                
            } else if (s[i] == '.') { // dot can only occur once and cannot occur after e/E
                if (!dotExisted && !eExisted) dotExisted = true;
                else return false;
            } else return false;
        }
        // Process the last char, it can only be digit or dot, when is dot, there should be no dot and e/E before and must follow a digit
        if (s[right] >= '0' && s[right] <= '9') return true;
        else if (s[right] == '.' && !dotExisted && !eExisted && digitExisited) return true;
        else return false;
    }
};

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Summary

  这道题目的分享到这里，感谢你的支持！