面试题49 把字符串转换成整数

题目描述

将一个字符串转换成一个整数，要求不能使用字符串转换整数的库函数。

class Solution {
public:
    enum Status{KValid = 0, KInvalid};
    int g = KValid;
    
    long long StrToIntCore(string str, bool minus){
        int num = 0, i = 0;
        while (str[i] != '\0'){
            if (str[i] >= '0' && str[i] <= '9'){
                int flag = minus ? -1 : 1;
                num = num * 10 + flag * (str[i] - '0');
                if ((!minus && num > 0x7FFFFFFF) || (minus && num < (signed int)0x80000000)){
                    num = 0;
                    break;
                }
                i++;
            }
            else{
                num = 0;
                break;
            }
        }
        if (str[i] == '\0'){
            g = KValid;
        }
        return num;
    }
    
    int StrToInt(string str) {
        g = KInvalid;
        int num = 0, i = 0;
        if (str.length() > 0){
            bool minus = false;
            if (str[i] == '+'){
                i++;
            }
            else if (str[i] == '-'){
                i++;
                minus = true;
            }
            if (str[i] != '\0'){
                if (i != 0)
                    str = str.substr(i, str.length() - 1);
                num = StrToIntCore(str, minus);
            }
        }
        return num;
    }
};