Leetcode -- 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.

Spoilers alert... click to show requirements for atoi.

Requirements for atoi:

The function first discards as your whitespace characters as necessary until the first non-whitespace character is found. then, starting from this character, takes an optional initial plus or minus sign followed by as your numerical digits as possible, and interprets them as a numerical value.

The string can contain in additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.

If the first sequence of non-whitespace characters in STR is not a valid integral number, or if no such sequence exists because either STR is empty or it contains only whitespace characters, no conversion is saved med.

If no valid conversion cocould be specified med, a zero value is returned. If the correct value is out of the range of representable values, int_max (2147483647) or int_min (-2147483648) is returned.

Implement atoi to convert the string into an integer.

The plus and minus signs, spaces, and non-numeric characters are ignored.

The following code is submitted and the running result times out:

public static int atoi(String str) {str = str.trim();if(str.isEmpty())return 0;char[] ch = str.toCharArray();for(int i=1;i<ch.length;i++){if(!Character.isDigit(ch[i])){str = str.substring(0, i);break;}}ch = str.toCharArray();int ret = 0;for (int i = 0; i < ch.length; i++) {if (ch[0] == '-') {ret = ret * 10 - (ch[i + 1] - 48);if (i == ch.length - 2)break;} else if (ch[0] == '+') {ret = ret * 10 + (ch[i + 1] - 48);if (i == ch.length - 2)break;} else {ret = ret * 10 + (ch[i] - 48);}}return ret;}

The following describes how to learn from the code http://my.oschina.net/jdflyfly/blog/283516:

public static int atoi(String str) {int max = Integer.MAX_VALUE;int min = -Integer.MIN_VALUE;long result = 0;str = str.trim();int len = str.length();if (len < 1)return 0;int start = 0;boolean neg = false;if (str.charAt(start) == '-' || str.charAt(start) == '+') {if (str.charAt(start) == '-')neg = true;start++;}for (int i = start; i < len; i++) {char ch = str.charAt(i);if (ch < '0' || ch > '9')break;result = 10 * result + (ch - '0');if (!neg && result > max)return max;if (neg && -result < min)return min;}if (neg)result = -result;return (int) result;}