leetcode string to integer

1, string.trim()将string中的空格去掉。

2，java 中有定义int的最大值和最小值，Integer.MAX_VALUE  Integer.MIN_VALUE

3,将char的值转换为integer的值， 就－‘0’

public class stringtoint {
    public int atoi(String str) {
        final int max = Integer.MAX_VALUE;
        final int min = Integer.MIN_VALUE;
        if (str == null) {
            return 0;
        }
        str = str.trim();
        if (str.length() == 0) {
            return 0;
        }
        int sign = 1;
        int i = 0;
        if (str.charAt(0) == ‘+‘) {
            sign = 1;
            i++;
        }
        if (str.charAt(0) == ‘-‘) {
            sign = -1;
            i++;
        }
        long temp = 0;
        for (; i < str.length(); i++) {
            if (str.charAt(i) < ‘0‘ || str.charAt(i) > ‘9‘) {
                break;
            }
            temp = temp * 10 + str.charAt(i) - ‘0‘;
            if (temp > max && sign == 1) {
                return max;
            }
        }
        if (temp * sign > max) {
            return max;
        }
        if (temp * sign < min) {
            return min;
        }
        return (int) temp * sign;
    }
}