LeetCode 8 String to Integer (string转int)

题目来源：https://leetcode.com/problems/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):
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解题思路：

照着要求写代码，可以总结如下：

1. 字串为空或者全是空格，返回0；

2. 字串的前缀空格需要忽略掉；

3. 忽略掉前缀空格后，遇到的第一个字符，如果是‘+’或‘－’号，继续往后读；如果是数字，则开始处理数字；如果不是前面的2种，返回0；

4. 处理数字的过程中，如果之后的字符非数字，就停止转换，返回当前值；

5. 在上述处理过程中，如果转换出的值超出了int型的范围，就返回int的最大值或最小值。

Java代码：

 public class Solution {
     public int myAtoi(String str) {
         int max = Integer.MAX_VALUE;
         int min = -Integer.MIN_VALUE;
         long result = 0;
         str = str.trim();
         int len = str.length();
         if (len < 1)
             return 0;
         int start = 0;
         boolean neg = false;

         if (str.charAt(start) == '-' || str.charAt(start) == '+') {
             if (str.charAt(start) == '-')
                 neg = true;
             start++;
         }

         for (int i = start; i < len; i++) {
             char ch = str.charAt(i);

             if (ch < '0' || ch > '9')
                 break;
             result = 10 * result + (ch - '0');
             if (!neg && result > max)
                 return max;
             if (neg && -result < min)
                 return min;

         }
         if (neg)
             result = -result;

         return (int) result;
     }

 };