[Leetcode 27] 65 Valid Number

Problem:

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.

Analysis:

So many cases to consider!

First of all, remove all the space at both ends of the given string;

Now we start from the left. 

The first position is a little bit special

1. '+/-': skip them

2. '.': set the dotFlag

3. '0~9': set the numFlag

4. others:  invalid input 

we continue 

if '.' is met, we break out of the current loop, start a new one. Note after '.', only 'e', numbers are allowed.

if 'e' is met, break out of the current loop, start a new one. Note after 'e', only numbers or '+/-' are allowed

Code:

class Solution {
public:
    bool isNumber(const char *s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int idx = 0, len = strlen(s)-1;
        bool dotFlag = false, numFlag = false, eFlag=false;
        
        if (s=="") return false;
        
        while (s[idx] == ' ') idx++;
        if (idx > len) return false;
        
        while (s[len] == ' ') len--;
        
        
        if (s[idx] == '+' || s[idx] == '-') idx++;
        
        if (idx > len) return false;
        
        int i;
        for (i=idx; i<=len; i++) {
            if (s[i] == 'e') {
                i += 1;
                eFlag = true;
                break;
            }
            
            if (s[i] == '.') {
                i += 1;
                dotFlag = true;
                break;
            }
            
            if (s[i]>='0' && s[i]<='9') {
               numFlag = true;
            } else {
                return false;
            }
            
        }
        
        
        if (dotFlag) {
            if (!numFlag && (i>len || ((s[i]<'0' && s[i]>'9') && s[i]!='e')))
                return false;
            
            for (; i<=len; ++i) {
                if (s[i] <'0' || s[i] > '9') {
                    if (s[i] == 'e') {
                        i+= 1;
                        eFlag = true;
                        break;
                    } else {
                        return false;
                    }
                }
                
                numFlag = true;
            }
        }
        
        //number after e
        if (eFlag) {
            if (!numFlag) return false;
            
            if (i==idx+1 || i>len) return false;
        
            if (s[i] == '+' || s[i] == '-')
                i += 1;
            
            if (i > len) return false;
            
            for (; i<=len; i++) {
                if (s[i]<'0' || s[i]>'9')
                    return false;
            }
        }
        
        
        return true;
    }
};

Attention: