valid number@leetcode

刷题必备书籍：Cracking the Coding Interview: 150 Programming Questions and Solutions 

简历：The Google Resume: How to Prepare for a Career and Land a Job at Apple, Microsoft, Google, or any Top Tech Company
算法学习书籍：Introduction to Algorithms
编程珠玑：Programming Pearls (2nd Edition)
C++ 学习：The C++ Programming Language, 4th Edition
经典操作系统书籍，龙书：Operating System Concepts
创业：The Start-up of You: Adapt to the Future, Invest in Yourself, and Transform Your Career

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.

这道题和string to integer有相似之处。主要就是各类情况都要考虑清楚。有人用finite automata 去做。我还是偏向于直接写代码。有一个地方卡了好久不过，也不晓得为什么。

	class Solution {
	public:
	bool isNumber(const char *s) {
	// Start typing your C/C++ solution below
	// DO NOT write int main() function
	if (s == NULL)
	return false;
	while(isspace(*s))
	s++;
	if (*s == '+' || *s == '-')
	s++;
	bool eAppear = false;
	bool dotAppear = false;
	bool firstPart = false;
	bool secondPart = false;
	bool spaceAppear = false;
	while(*s != '\0')
	{
	if (*s == '.')
	{
	if (dotAppear || eAppear || spaceAppear)
	return false;
	else
	dotAppear = true;
	}
	else if (*s == 'e' || *s == 'E')
	{
	if (eAppear || !firstPart || spaceAppear)
	return false;
	else
	eAppear = true;
	}
	else if (isdigit(*s))
	{
	if (spaceAppear)
	return false;
	if (!eAppear)
	firstPart = true;
	else
	secondPart = true;
	}
	else if (*s == '+' || *s == '-')
	{
	if (spaceAppear)
	return false;
	if (!eAppear || !(*(s-1) == 'e' || *(s-1) == 'E'))
	return false;
	}
	else if (isspace(*s))
	spaceAppear = true;
	else
	return false;
	s++;
	}
	if (!firstPart)
	return false;
	else if (eAppear && !secondPart)
	return false;
	else
	return true;
	}
	};

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