8. 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.

题目含义：实现atoi功能

 

    public int myAtoi(String str) {
    if (str == null || str.length() == 0)
        return 0;//
    str = str.trim();
    char firstChar = str.charAt(0);
    int sign = 1, start = 0, len = str.length();
    long sum = 0;
    if (firstChar == '+') {
        sign = 1;
        start++;
    } else if (firstChar == '-') {
        sign = -1;
        start++;
    }
    for (int i = start; i < len; i++) {
        if (!Character.isDigit(str.charAt(i)))
            return (int) sum * sign;
        sum = sum * 10 + str.charAt(i) - '0';
        if (sign == 1 && sum > Integer.MAX_VALUE)
            return Integer.MAX_VALUE;
        if (sign == -1 && (-1) * sum < Integer.MIN_VALUE)
            return Integer.MIN_VALUE;
    }

    return (int) sum * sign;        
    }