LeetCode Q65: Valid Number (hard)

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.

My solution is tedious, and I consider three possibilities separately.

	class Solution {
	public:
	bool isInt(string s){
	for(int i=0; i<s.length(); ++i){
	int c=s[i]-'0';
	if(c>9||c<0){
	if((s[i]=='+'||s[i]=='-')&&i==0&&i!=s.length()-1)
	continue;
	return false;
	}
	}
	return true;
	}
	bool isFloat(string s){
	int pofpt=-1;
	for(int i=0; i<s.length(); i++){
	if(s[i]=='.'){
	pofpt=i;
	break;
	}
	}
	if(pofpt==-1||(s.length()==1))
	return false;
	string s0=s.substr(0, pofpt);
	string s1=s.substr(pofpt+1, s.length()-pofpt);
	bool r0=isInt(s0);
	bool r1=isInt(s1);
	if(s0.length()==1&&(s0[0]=='-'||s0[0]=='+'))
	r0=true;
	if(s1[0]=='-'||s1[0]=='+')
	r1=false;
	if((s0[s0.length()-1]=='-'||s0[s0.length()-1]=='+')&&s1.empty())
	return false;
	return r0&&r1;
	}
	bool isSci(string s){
	int pofe=-1;
	for(int i=0; i<s.length(); i++){
	if(s[i]=='e'){
	pofe=i;
	break;
	}
	}
	if(pofe==0||pofe==s.length()-1||pofe==-1)
	return false;
	string s0=s.substr(0, pofe);
	string s1=s.substr(pofe+1, s.length()-pofe);
	bool r0=(isInt(s0)||isFloat(s0));
	bool r1=isInt(s1);
	return r0&&r1;
	}
	bool isNumber(string s) {
	if(s.length()==0)
	return false;
	int p=0;
	for(;p<s.length(); p++){
	if(s[p]!=' ')
	break;
	}
	s.erase(s.begin(), s.begin()+p);
	p=s.length()-1;
	for(; p>=0; p--){
	if(s[p]!=' ')
	break;
	}
	s.erase(s.begin()+p+1, s.end());
	if(s.length()==0)
	return false;
	bool r0=isInt(s);
	bool r1=isFloat(s);
	bool r2=isSci(s);
	return (r0||r1||r2);
	}
	};

view raw Q65ValidNumber.cpp hosted with ❤ by GitHub

A relatively simple solution is given by someone's post on LeetCode's forum:

	class Solution {
	public:
	bool isNumber(string s) {
	int i = 0, n = s.length();
	// Skip the leading spaces
	while (i < n && isspace(s[i])) i++;
	// Skip the sign
	if (s[i] == '+' || s[i] == '-') i++;
	// Check for the following significant parts
	int digits = 0, dots = 0;
	while (i < n && (isdigit(s[i]) || s[i] == '.')) {
	if (isdigit(s[i])) digits++;
	else dots++;
	i++;
	}
	if (digits < 1 || dots > 1) return false;
	if (i == n) return true;
	// Check for the exponential parts
	if (s[i] == 'e') {
	i++;
	if (i == n) return false;
	if (s[i] == '+' || s[i] == '-') i++;
	digits = 0;
	while (i < n && (isdigit(s[i]))) {
	digits++;
	i++;
	}
	if (digits < 1) return false;
	}
	// Skip the trailing spaces
	while (i < n && isspace(s[i])) i++;
	return i == n;
	}
	};

view raw Q65-2.cpp hosted with ❤ by GitHub