[Leetcode8]字符串转整数 (atoi)

实现 atoi，将字符串转为整数。

这个代码写得太恶心了，等忙完论文一定改改。

python:

class Solution(object):
    def myAtoi(self, str):
        """
        :type str: str
        :rtype: int
        """
        index = 0
        res = ""
        str = str.lstrip()
        l = len(str)
        if l==0:
            return 0
        elif str[index] == "+":
            index += 1
            while(index<l):
                if(ord(str[index])>=48 and ord(str[index])<=57):
                    res += str[index]
                    index += 1
                else:
                    break
            if res == "":
                return 0
        elif str[index] == "-":
            res += str[index]
            index += 1
            while(index<l):
                if(ord(str[index])>=48 and ord(str[index])<=57):
                    res += str[index]
                    index += 1
                else:
                    break
            if res == "-":
                return 0
        elif (ord(str[index])>=48 and ord(str[index])<=57):
            while(index<l):
                if(ord(str[index])>=48 and ord(str[index])<=57):
                    res += str[index]
                    index += 1
                else:
                    break
        else:
            return 0
        result = int(res)
        if result>(2**31-1):
            return 2**31-1
        elif result<-(2**31):
            return -(2**31)
        return int(res)

C++,我在用string索引时总是报错，我就先将string转成char然后索引比较ASCII，最后用了istringstream转成int。

class Solution {
public:
    int myAtoi(string str) {
        int start = 0;
        int l = str.length();
        if(l==0){
            return 0;
        }
        char s[l];
        for(int i=0;i<l;i++){
            s[i] = str[i];
        }
        string res = "";
        while(s[start]==32){
            start += 1;
            if(start == l){
                return 0;
            }
        }
        if(s[start]==43){
            start += 1;
            while(start<l){
                if(s[start]>=48 && s[start]<=57){
                    res += str[start];
                    start += 1;
                }
                else{
                    break;
                }
            }
            if(res.length() == 0){
                return 0;
            }
        }
        else if(s[start]==45){
            res += "-";
            start += 1;
            while(start<l){
                if(s[start]>=48 && s[start]<=57){
                    res += str[start];
                    start += 1;
                }
                else{
                    break;
                }
            }
            if(res.length() == 1){
                return 0;
            }
        }
        else if(s[start]>=48 && s[start]<=57){
            res += str[start];
            start += 1;
            while(start<l){
                if(s[start]>=48 && s[start]<=57){
                    res += str[start];
                    start += 1;
                }
                else{
                    break;
                }
            }
        }
        else{
            return 0;
        }
        istringstream ss(res);
        int y;
        ss >> y;
        if(y>INT_MAX){
            return INT_MAX;
        }
        else if(y<INT_MIN){
            return INT_MIN;
        }
        else{
            return y;
        }
    }
};