String to Integer (atoi)
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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.
class Solution { public: // 字符串转int,注意判断超出Int范围 int myAtoi(string str) { if (str == "") return 0; // 去首尾空格 str.erase(0, str.find_first_not_of(‘ ‘)); str.erase(str.find_last_not_of(‘ ‘) + 1); int i = 0, len = str.length(), sign = 1; while ( i < len && str[i] == ‘ ‘) i++; if (i == len) return 0; if (str[i] == ‘+‘) { sign = 1; i++; } else if (str[i] == ‘-‘) { sign = -1; i++; } // 转换结果可能超出int范围,使用long long作为转换后接收变量的类型 long long ret = 0; for (; i < len; i++) { if (str[i] < ‘0‘ || str[i] > ‘9‘) break; ret = ret * 10 + (str[i] - ‘0‘); if (ret > INT_MAX) break; } ret *= sign; if (ret > INT_MAX) return INT_MAX; if (ret < INT_MIN) return INT_MIN; return ret; } };
注释:
erase函数的原型如下:
(1)string& erase ( size_t pos = 0, size_t n = npos );
(2)iterator erase ( iterator position );
(3)iterator erase ( iterator first, iterator last );
也就是说有三种用法:
(1)erase(pos,n); 删除从pos开始的n个字符,比如erase(0,1)就是删除第一个字符
(2)erase(position);删除position处的一个字符(position是个string类型的迭代器)
(3)erase(first,last);删除从first到last之间的字符(first和last都是迭代器)
以下是库函数的定义:
stl: template<typename _Category, typename _Tp, typename _Distance = ptrdiff_t, typename _Pointer = _Tp*, typename _Reference = _Tp&> struct iterator { /// One of the @link iterator_tags tag [email protected] typedef _Category iterator_category; /// The type "pointed to" by the iterator. typedef _Tp value_type; /// Distance between iterators is represented as this type. typedef _Distance difference_type; /// This type represents a pointer-to-value_type. typedef _Pointer pointer; /// This type represents a reference-to-value_type. typedef _Reference reference; }; string: iterator erase(iterator __first, iterator __last); #if __cplusplus >= 201103L /** * @brief Remove the last character. * * The string must be non-empty. */ void pop_back() // FIXME C++11: should be noexcept. { erase(size()-1, 1); }
erase(iterator __first, iterator __last);
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