LeetCode - 8. String to Integer (atoi) 8. String to Integer (atoi) Problem's Link

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Mean: 

給你一個字元串，讓你将其轉換為數字.

analyse:

注意細節，坑點有點多.

Time complexity: O(N)

view code

class Solution

{

public:

   int myAtoi(string str)

   {

       int ret = 0, sign = 1, i = str.find_first_not_of(' '), base = INT_MAX / 10;

       if (str[i] == '+' || str[i] == '-') sign = str[i++] == '+' ?: -1;

       while (isdigit(str[i]))

       {

           if (ret > base || (ret == base && str[i] - '0' > 7))

               return sign > 0 ? INT_MAX : INT_MIN;

           ret = 10 * ret + (str[i++] - '0');

       }

       return sign * ret;

   }

};