Leetcode(93) Restore IP Addresses

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Description

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

Example:

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Input: "25525511135"
Output: ["255.255.11.135", "255.255.111.35"]

解法

暴力搜索三个点的位置，然后对分割后的ip进行检测即可。

注意check函数的写法

具体代码如下：

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class Solution {
    public List<String> restoreIpAddresses(String s) {
        List<String> res = new ArrayList<>();
        String ip1, ip2, ip3, ip4;
        if (s.length() > 12) {
            return res;
        }
        for (int i = 0; i < s.length(); i++) {
            for (int j = i + 1; j < s.length(); j++) {
                for (int k = j + 1; k < s.length() - 1; k++) {
                    ip1 = s.substring(0, i + 1);
                    ip2 = s.substring(i + 1, j + 1);
                    ip3 = s.substring(j + 1, k + 1);
                    ip4 = s.substring(k + 1);
                    if (check(ip1) && check(ip2) && check(ip3) && check(ip4)) {
                        String ip = ip1 + "." + ip2 + "." + ip3 + "." + ip4;
                        res.add(ip);
                    }
                }
            }
        }

        return res;
    }

    Boolean check(String ip) {
        int val = Integer.parseInt(ip);
        if (ip.charAt(0) == '0') {
            return ip.length() == 1;
        }
        return val <= 255;
    }
}