LC 8. 字符串转换整数 (atoi)

代码 :

class Solution {
public:
    int myAtoi(string str) {
        // trim all leading 0;
        int l = 0; 
        while(l < str.size() && str[l] == ' ') {
            l ++;
        }
        if(l == str.size()) {
            return 0;
        }
        // check the sign 
        int sign = 1; 
        if (str[l] == '-') {
            sign = -1;
            l ++ ;
        }
        else if (str[l] == '+') {
            sign = 1; 
            l ++ ;
        }
        // parse the integer
        int res = 0; 
        while(l < str.size() && isdigit(str[l])) {
            int digit = str[l] - '0';
            // res * 10 + digit > INT_MAX
            if(sign == 1 && (res > (INT_MAX - digit) / 10) ) {
                return INT_MAX;
            }
            // -res * 10 - digit < INT_MIN
            else if (sign == -1 && (-res < (INT_MIN + digit) / 10)  ) {
                return INT_MIN;
            }
            // [-2^31, 2^31 - 1]
            if( -res * 10 - digit == INT_MIN) 
                return INT_MIN;
            res = res * 10 + digit; 
            l ++ ;
        }
        res *= sign; 
        return res; 
    }
};

class Solution {
public:
    int myAtoi(string s) {
        /* skip all leading space */
        int l = 0;
        while(l < s.size() && s[l] == ' ') 
            l ++; 
        if(l == s.size()) return 0;
        /* check the sign of int */
        int sign = 1; 
        if(s[l] == '-') sign = -1, l ++; 
        else if (s[l] == '+') l ++;
        long long res = 0;
        while(l < s.size() && isdigit(s[l])) {
            res = res * 10 + s[l] - '0';
            l ++ ;
            if(res > INT_MAX) break;
        }
        res *= sign;
        if(res > INT_MAX) return INT_MAX; 
        if(res < INT_MIN) return INT_MIN; 
        return res;
    }
};