p8

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LeetCode p8 String to Integer (atoi) 题解

1.题目：

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.

Update (2015-02-10):
The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

题意：

输入一个字符串，输出它对应的数字。

2.解题思路:

考虑各种边界条件和非法输入。

3.代码

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public class Solution {
    public int myAtoi(String str) {
        char[] c = str.toCharArray();
		int ans = 0;
		int flag = 1;
		int i = 0;
		if (c.length < 1)
			return 0;
		while (c[i] == ' ' && i < str.length()) {
			i++;
		}
		if (c[i] == '+' || c[i] == '-') {
			flag = c[i] == '+' ? 1 : -1;
			i++;
		}

		for (; i < str.length(); i++) {
			if (c[i] >= '0' && c[i] <= '9') {
				if (ans > Integer.MAX_VALUE / 10
						|| (Integer.MAX_VALUE / 10 == ans && Integer.MAX_VALUE % 10 < c[i] - '0')) {
					if (flag == 1)
						return Integer.MAX_VALUE;
					else {
						return Integer.MIN_VALUE;
					}
				}
				ans = ans * 10 + c[i] - '0';
			} else {
				return flag * ans;
			}
		}
		// System.out.println(flag);
		return flag * ans;
	}
}

4.一些总结：