[leetcode] String to Integer (atoi)

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于 2013-08-16 23:06:33 发布

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本文介绍了一个C++实现的atoi函数，用于将字符串转换为整数。文章详细展示了如何处理各种输入情况，包括前导空格、正负号及非法字符等。

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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.

class Solution {
public:
    int atoi(const char *str) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int revalue=0;
        int i=0 , flag=1 , len=strlen(str);
        for( ; i<len && str[i]==' ';  i++);
        if(i==len)
            return revalue;
        if(str[i]=='-'){
            flag=-1;
            i++;
        }
        if(str[i]=='+')
            i++;
        int tmp=0;
        if(flag==1){
            for( ; i<len ; i++){
                if(str[i]<'0' || str[i]>'9'){
                    return tmp;
                }
                int inner=tmp;
                tmp=tmp*10+str[i]-'0';
                if(tmp/10!=inner)
                    return 2147483647;
            }//but how can we judge if it's overflow
        }else{
            for(; i<len ; i++){
                if(str[i]<'0' || str[i]>'9')
                    return tmp;
                int inner=tmp;
                tmp=10*tmp-(str[i]-'0');
                if(tmp/10!=inner)
                    return -2147483648;
            }
        }
        return tmp;
    }
};