学步园

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.

思路：这道题就是思考各种情况，我提交的时候漏过8种非法的数字，才AC了。

class Solution {
public:
    bool isNumber(const char *s) {
        int len = strlen(s);
        int i,j,k;
        int point = 0;
        int science = 0;
        int co = 0;
        for(i=0; i<len; ++i)
        {
            if(s[i] != ' ')
            {
                if (s[i] == '+' || s[i] == '-')
                {
                    ++i;
                }    
                break;
            }
        }
        if (i == len)
        {
            return false;
        }
        for(; i<len; ++i)
        {
            if (s[i] != '.' && s[i] != 'e' && (s[i]-'0'>9 || s[i] -'0'<0) && s[i] != ' ')
            {
                return false;
            }
            else if(s[i] == ' ')
            {
                for(k=i+1; k<len; ++k)
                {
                    if(s[k] != ' ')
                    {
                        return false;
                    }
                }
            }
            else
            {
                if (s[i] == '.')
                {
                    point++;
                    if (science > 0)
                    {
                        return false;
                    }    
                    if (i-1>=0 && s[i-1]-'0'>=0 && s[i-1]-'0'<=9)
                    {
                        co++;
                    }    
                    if (i+1<len && s[i+1]-'0'>=0 && s[i+1]-'0'<=9)
                    {
                        co++;
                    }    
                    if (co == 0)
                    {
                        return false;
                    }    
                }
                else if (s[i] == 'e')
                {
                    science++;
                    if (i+1 >= len || i-1 < 0)
                    {
                        return false;
                    }    
                    if ((s[i+1]-'0'<0 || s[i+1]-'0'>9) && s[i+1]!='+' && s[i+1]!='-')
                    {
                        return false;
                    }    
                    if (s[i+1] == '+' || s[i+1] == '-')
                    {
                        if (i+2 >= len)
                        {
                            return false;
                        }    
                        if (s[i+2]-'0'>9 || s[i+2]-'0'<0)
                        {
                            return false;
                        }    
                        i += 2;
                        continue;
                    }    
                    if (s[i-1]!='.' && (s[i-1]-'0'<0 || s[i-1]-'0'>9))
                    {
                        return false;
                    }    
                }
                if(point >= 2 || science >= 2)
                {
                    return false;
                }
            }
        }
        return true;
    }
};