LeetCode(8)--String to Integer (atoi)

題目如下：
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.

解題思路：
首先，要判斷該字符串是否可以還換成int類型，然後，判斷字符的符號（測試集中有-和+），最後將字符傳中的數逐個取出即可。

提交的代碼：

    public int myAtoi(String str) {
        int p = 0, ret = 0;
        while(p < str.length() && Character.isWhitespace(str.charAt(p))) ++p;
        if(p == str.length()) return 0;
        boolean negFlag = (str.charAt(p) == '-');
        if(str.charAt(p) == '+'  || str.charAt(p) == '-') ++p;
        for(; p<str.length(); ++p) {
            if(str.charAt(p) > '9' || str.charAt(p) < '0') {
                break;
            }else {
                int digit = str.charAt(p) - '0';
                if(!negFlag && ret > (Integer.MAX_VALUE - digit) /10) 
                     return Integer.MAX_VALUE;
                else if(negFlag && ret < (Integer.MIN_VALUE + digit)/10) 
                     return Integer.MIN_VALUE;
                ret = ret * 10 + (negFlag? -digit: digit);
            }
        }
        return ret;
    }