LeetCode题解：Restore IP Addresses

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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)

题意：给定一个字符串，判断其代表的IP地址数

解决思路：类似穷举……

代码：

public class Solution {    public List<String> restoreIpAddresses(String s) {        List<String> res = new ArrayList<String>();        int len = s.length();        for(int i = 1; i<4 && i<len-2; i++){            for(int j = i+1; j<i+4 && j<len-1; j++){                for(int k = j+1; k<j+4 && k<len; k++){                    String s1 = s.substring(0,i), s2 = s.substring(i,j), s3 = s.substring(j,k), s4 = s.substring(k,len);                    if(isValid(s1) && isValid(s2) && isValid(s3) && isValid(s4)){                        res.add(s1+"."+s2+"."+s3+"."+s4);                    }                }            }        }        return res;    }    public boolean isValid(String s){        if(s.length()>3 || s.length()==0 || (s.charAt(0)=='0' && s.length()>1) || Integer.parseInt(s)>255)            return false;        return true;    }}

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