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8. String to Integer (atoi)

8. String to Integer (atoi)

作者: Al73r | 来源:发表于2017-09-19 13:46 被阅读0次

    题目

    Implement atoi to convert a string to an integer.
    Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.
    Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.
    **Update (2015-02-10):
    **The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.
    spoilers alert... click to show requirements for atoi.

    思路

    题目故意出得很模糊,且鼓励不看具体要求直接写。那就慢慢改进吧。
    最后总结下这道题的步骤为:处理空格、处理正负号、处理最前面的零、处理数字、处理溢出、处理结束。

    实现

    class Solution {
    public:
        int myAtoi(string str) {
            long long ans=0;
            int sign=1, i=0;
            while(str[i]==' ') i++;
            if(str[i]=='-'){
                sign *= -1;
                i++;
            }
            else if(str[i]=='+')
                i++;
            if(str[i]=='-' || str[i]=='+') return 0;
            while(str[i]=='0') i++;
            for(; i<str.size() && str[i]>='0' && str[i]<='9' ; i++){
                ans = ans*10 + (str[i]-'0');
                if(sign>0 && ans > INT_MAX) return INT_MAX;
                if(sign<0 && ans > (-(long long)INT_MIN)) return INT_MIN;
            }
            return ans*sign;
        }
    };
    

    思考

    本来还想着去写十六进制和八进制的字符串,但是发现根本没用=_=
    这题有点刁钻了其实,所以大家都给了差评,哈哈。
    不过考察的内容还可以,主要是细心就行了。

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