LeetCode 8:String to Integer (atoi)

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.

代码如下：

class Solution {
public:
    long strtol(const char *nptr, char **endptr, int base)
		{
			const char * s;
			long acc, cutoff;
			int neg, any, cutlim;
			int c;
			if (base<0 || base==1 || base>36)
			{
				if (endptr!=0)
					*endptr = (char*)nptr;
				return 0;
				
			}
			s = nptr;
			do 
			{
				c = (unsigned char) *s++;
			} while(isspace(c));
			if (c == '-')
			{
				neg = 1;
				c = *s++;
			} 
			else
			{
				neg = 0;
				if ( c=='+')
					c = *s++;
			}
			if ((base==0 || base==16) &&c=='0' &&(*s =='x' || *s == 'X'))
			{
				c = s[1];
				s+=2;
				base = 16;
			}
			if (base == 0)
			{
				base = c=='0' ? 8:10;
			}
			cutoff = neg? LONG_MIN:LONG_MAX;
			cutlim = cutoff %base;
			cutoff /= base;
			if (neg )
			{
				if (cutlim > 0)
				{
					cutlim -=  base;
					cutoff += 1;
				}
				cutlim = -cutlim;
			}
			for (acc =0, any=0;;c=(unsigned char)*s++)
			{
				if (isdigit(c))
					c -= '0';
				else if (isalpha(c))
					c -= isupper(c) ? 'A'-10 : 'a'-10;
				else 
					break;
				if (c >= base)
					break;
				if(any < 0)
					continue;
				if (neg)
				{
					if (acc < cutoff || (acc==cutoff && c>cutlim))
					{
						any = -1;
						acc = LONG_MIN;
					} 
					else
					{
						any = 1;
						acc *= base;
						acc -= c;
					}
				} 
				else
				{
					if (acc>cutoff || (acc==cutoff && c>cutlim))
					{
						any = -1;
						acc = LONG_MAX;
					} 
					else
					{
						any = 1;
						acc *= base;
						acc += c;
					}
				}
			}
			if(endptr != 0)
				*endptr = (char *)(any? s-1:nptr);
			return acc;

		}
    int atoi(const char *str) {
        return strtol(str, NULL, 10);
    }
};