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class Solution {
public:
    bool isNumber(const char *s) {
        string str = "";
        int len = strlen(s);
        int i = 0;
        for(;i < len;i++) {
            if(s[i] == ' ')continue;
            else break;
        }
        for(;i < len;i++) {
            str.push_back(s[i]);
        }
        for(int i = str.length()-1;i >= 0;i--) {
            if(str[i] == ' ') {
                str.erase(i);
            }
            else
                break;
        }
        return isNumberString(str);
    }
private:
    bool isNumberString(string s) {
        // Does it have a sign?
        // Does it have a decimal point?
        // Does it contain 'e'?
        // Does it have leading zeros?
        int len = s.length();
        if(len <= 0)return false;
        if(len == 1) {
            if(s[0] < '0' || s[0] > '9')return false;
            else return true;
        }
        int start = 0;
        if(s[0] == '+' || s[0] == '-') {
            start = 1;
        }
        bool isZeroAllowed = true;
        bool isPotAllowed = false;
        bool isEallowed = false;

        bool once = true;

        if(s[start] == '.') {
            if(len >= start + 2) {
                if(s[start + 1] >= '0' && s[start + 1] <= '9') {
                    isZeroAllowed = true;
                    isPotAllowed = false;
                    isEallowed = true;
                    once = false;
                    start = start + 2;  
                }
                else
                    return false;
            }
            else 
                return false;
        }
        for(int i = start;i < len;i++) {
            if(s[i] == '.' && isPotAllowed == false) {
                return false;
            }
            if(s[i] == '.' && isPotAllowed == true) {
                isPotAllowed = false;
                continue;
            }
            if(s[i] == 'e' && isEallowed == false) {
                return false;
            }
            if(s[i] == 'e' && isEallowed == true) {
                isEallowed = false;
                isPotAllowed = false;
                once = false;
                if(i + 1 >= len)return false;
                if(s[i+1] == '-' || s[i+1] == '+') {
                    if(i+2 >= len)return false;
                    if(s[i+2] < '0' || s[i+2] > '9')return false;
                    i+=2;
                    continue;
                } 
                if(s[i+1] < '0' || s[i+1] > '9')return false;
                continue;
            }
            if(s[i] >= '0' && s[i] <= '9') {
                if(once == true) {
                    isZeroAllowed = true;
                    isPotAllowed = true;
                    isEallowed = true;

                    once = false;
                }
                continue;
            }
            return false;
        }
        return true;
    }
};