Restore IP Addresses leetcode java

题目：

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

For example:
Given "25525511135",

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

题解：

利用循环递归解决子问题。对于每个段内数来说，最多3位最少1位，所以在每一层可以循环3次，来尝试填段。因为IP地址最多4个分段，当层数是3的时候说明已经尝试填过3个段了，那么把剩余没填的数段接到结尾即可。

这个过程中要保证的是填的数是合法的，最后拼接的剩余的数也是合法的。

注意开头如果是0的话要特殊处理，如果开头是0，判断整个串是不是0，不是的话该字符就是非法的。因为001，01都是不对的。

代码如下：

1     public ArrayList<String> restoreIpAddresses(String s) {
2         ArrayList<String> res = new ArrayList<String>();
3         String item = new String();
4         if (s.length()<4||s.length()>12)
5         return res;
6
7         dfs(s, 0, item, res);
8         return res;
9     }
10
11     public void dfs(String s, int start, String item, ArrayList<String> res){
12         if (start == 3 && isValid(s)) {
13             res.add(item + s);
14             return;
15         }
16         for(int i=0; i<3 && i<s.length()-1; i++){
17             String substr = s.substring(0,i+1);
18             if (isValid(substr))
19                 dfs(s.substring(i+1, s.length()), start+1, item + substr + '.', res);
20         }
21     }
22
23     public boolean isValid(String s){
24         if (s.charAt(0)=='0')
25             return s.equals("0");
26             int num = Integer.parseInt(s);
27
28         if(num <= 255 && num > 0)
29             return true;
30         else
31             return false;
32     }

Refrence：http://blog.csdn.net/u011095253/article/details/9158449

转载于:https://www.cnblogs.com/springfor/p/3886409.html

Restore IP Addresses leetcode java相关推荐

[LeetCode]93.Restore IP Addresses
题目 Given a string containing only digits, restore it by returning all possible valid IP address comb ...
【DFS + backtrack】LeetCode 93. Restore IP Addresses
LeetCode 93. Restore IP Addresses Solution1:我的答案怎么就这么慢... class Solution { public:vector<string& ...
[LeetCode] Restore IP Addresses 复原IP地址
Given a string containing only digits, restore it by returning all possible valid IP address combina ...
[LeetCode] Restore IP Addresses 复原IP地址
Given a string containing only digits, restore it by returning all possible valid IP address combina ...
[leetcode] Restore IP Addresses
这个题目就和Palindrome Partitioning很像了,而且比那个的DFS的递归要简单一些,让常人更好理解一些.但是边界条件更多,要考虑清楚. 整体思路就是深度优先搜索,首先看到边界条件没, ...
LeetCode:Restore IP Addresses
Given a string containing only digits, restore it by returning all possible valid IP address combina ...
LeetCode 93. Restore IP Addresses
Given a string containing only digits, restore it by returning all possible valid IP address combina ...
【leetcode刷题笔记】Restore IP Addresses
Given a string containing only digits, restore it by returning all possible valid IP address combina ...
LeetCode Restore IP Addresses(回溯法)
题意:给出一个由数字组成的字符串,求其能表示的ip地址列表注意不能有前缀0,如010 思路:每次操作时,有两种情况,一种是添加点,一种是将其作为当前数的后序数. 在小数点的个数超过3时,递归退出. ...

Restore IP Addresses leetcode java

Restore IP Addresses leetcode java相关推荐

最新文章

热门文章