Restore IP address

来源：互联网发布：熹妃传刷元宝软件编辑：程序博客网时间：2024/05/19 22:49

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

For example:
Given "25525511135",

return ["255.255.11.135","255.255.111.35"]. (Order does not matter)

2014.8.9update:

出错的地方：

1.检查最后一个ip时，注意字符串开始为‘0’的情况：如果长度>1那么检测失败；否则为数字0，加入最后结果

2.检测非最后一个ip时，for (i = 0; i < s.length(); i++)注意S的长度可能小于3，所以要加上&&i

    public List<String> restoreIpAddresses(String s) {        List<String> result = new ArrayList<String>();        if (s.length() > 12) {            return result;        }        helper(result, s, "", 0);        return result;    }        void helper(List<String> result, String s, String last, int pos) {        if (pos == 4 && s.isEmpty()) {            result.add(last);            return;        } else if (s.isEmpty()) {            return;        } else if (s.charAt(0) == '0') {            helper(result, s.substring(1), last + (pos == 0 ? "0" : ".0"), pos+1);            return;        }        for (int i = 0; i < 3 && i < s.length(); i++) {            String str = s.substring(0, i+1);            if (Integer.valueOf(str) < 256) {                String tmp = last + (pos == 0 ? "" : ".") + str;                helper(result, s.substring(i+1), tmp, pos+1);            }        }    }

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