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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.

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);    }};

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