LeetCode题解：Restore IP Addresses

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;
}
}