題目如下：

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.

這道題簡單是挺簡單的，關鍵是你要考慮到它的各種情況，比如越界，空格等等情況，我試了好久才搞定。。。刷的快吐了

public class Solution {
    public int myAtoi(String str) {
        long result = 0;
		boolean flag = false;
		int i = 0;
		while (i < str.length() && str.charAt(i) == ' ')
			i++;
		if (i < str.length() && str.charAt(i) == '-') {
			flag = true;
			i++;
		}else if (i < str.length() && str.charAt(i) == '+') {
			i++;
		}
		while (i < str.length() && str.charAt(i) >= '0' && str.charAt(i) <= '9') {
			result = result * 10 + str.charAt(i) - '0';
			if((flag && result<Integer.MIN_VALUE) || result>Integer.MAX_VALUE) break;
			i++;
		}

		if (flag) {
			result = result * -1;
			if (result < Integer.MIN_VALUE)
				return Integer.MIN_VALUE;
			else {
				return (int) result;
			}
		} else {
			if (result > Integer.MAX_VALUE)
				return Integer.MAX_VALUE;
			else {
				return (int) result;
			}
		}
    }
}