LeetCode：atoi函数 被折腾惨了

主要是情况太多了。。。。

public int atoi(String str) {int num = 0;int sign = 1;int j = 0;while (j < str.length()) {if (str.startsWith(" ")) {str = str.substring(1);j++;} elsebreak;}if (str.startsWith("+"))str = str.substring(1);if (str.startsWith("-")) {str = str.substring(1);sign = -1;}int n = str.length();for (int i = 0; i < n; i++) {if (str.charAt(i) < '0' || str.charAt(i) > '9')break;int x = str.charAt(i) - '0';if (num > Integer.MAX_VALUE / 10|| (num == Integer.MAX_VALUE / 10 && x > Integer.MAX_VALUE % 10)) {return sign == -1 ? Integer.MIN_VALUE : Integer.MAX_VALUE;}num = num * 10 + x;}return num * sign;}