Sword finger offer 20 String representing numeric value

Original link ： The finger of the sword Offer 20. String representing the value

 

solution:

class Solution {
public:
    bool isNumber(string s) {
        // String empty direct return 
        if(s.empty()) return false;
        int i = 0,j = s.size() - 1;
        while(s[i] == ' ' && i < j) i++;
        while(s[j] == ' ' && i < j) j--;
        s = s.substr(i, j - i + 1); // Remove the head and tail 0

        bool numFlag = false;
        bool dotFlag = false;
        bool eFlag = false;

        for(int i = 0;i < s.size();i++) {
            if(s[i] >= '0' && s[i] <= '9') {    // It's a number , Mark numFlag
                numFlag = true;
            } else if(s[i] == '.' && !dotFlag && !eFlag) {  // Judged as . There is no need before . and e, Mark dotFlag
                dotFlag = true;
            } else if((s[i] == 'e' || s[i] == 'E') && !eFlag && numFlag) {  // determine e or E Appearance , Need not appear before e And numbers have appeared 
                eFlag = true;
                numFlag = false;
            } else if((s[i] == '+' || s[i] == '-') && (i == 0 || s[i - 1] == 'e' || s[i - 1] == 'E')) { // determine + or - Appearance , Can only appear in the first place or e Behind 

            } else return false;
        }
        return numFlag;
    }
};