LeetCode(8) String to Integer (atoi)解题报告

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字符转数字

问题:

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.

翻译:

实现atoi(c语言的字符串转数字函数)将字符串转换为整数
仔细的考虑所有可能出现的情况。

解题方案:

这道题感觉出的不是很好，提示给的不够。代码比较容易，主要考虑越界的情况。

public int myAtoi(String str) {
        if (str == null || str.trim().length() == 0) return 0;
        str = str.trim();
        int result = 0;
        int flag = 1;
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            if (i == 0) {
                if (c == '+') {
                } else if (c == '-') {
                    flag = -1;
                } else if (c >= '0' && c <= '9') {
                    result = result * flag + (c - '0') * flag;
                } else {
                    return 0;
                }
            } else {
                if (c >= '0' && c <= '9') {
                    int before = result;
                    result = result * 10 + (c - '0') * flag;
                    if (before > 0 && (Integer.MAX_VALUE - (c - '0') * flag) / 10 < before) {
                        return Integer.MAX_VALUE;
                    }
                    if (before < 0 && (Integer.MIN_VALUE - (c - '0') * flag) / 10 > before) {
                        return Integer.MIN_VALUE;
                    }
                } else {
                    break;
                }
            }


        }
        return result;
    }