8. String to Integer (atoi) Java Solutin

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.

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题意：

实现 atoi,将字符串转化为整数。

注意考虑所有可能的情况。

算法分析：

1.
先去掉多余的空格字符，从第一个非空格字符开始。

2.
按顺序读数字，如果出现下面三种情况则结束：

2.1
异常字符出现（异常字符跳过不计）。

2.2
数字越界（返回最接近的整数）。

2.3
字符串结束

 1 public class Solution {
 2     public int myAtoi(String str) {
 3         if(str == null) return 0;
 4         str = str.trim();
 5         if(str.length() == 0) return 0;
 6         Boolean isNex = false;
 7         int i = 0;
 8         if(str.charAt(0) == '+' || str.charAt(0) == '-'){
 9             i++;
10             if(str.charAt(0) == '-')
11                 isNex = true;
12         }
13         long result = 0;//若定义为int，边界值将会溢出。
14         for(;i<str.length();i++){
15             if(str.charAt(i) > '9' || str.charAt(i) < '0')
16                 break;
17             result = result*10 + str.charAt(i) - '0';
18             if(result > Integer.MAX_VALUE && !isNex)
19                 return Integer.MAX_VALUE;
20             if(-result < Integer.MIN_VALUE && isNex)
21                 return Integer.MIN_VALUE;
22         }
23         if(!isNex) return (int) result;
24         else result = -result;
25         return (int)result;
26     }
27 }