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)
public class Solution {
public List<String> restoreIpAddresses(String s) {List<String> res = new ArrayList<String>();
if(null == s || s.length() < 4 || s.length() > 12){
return res;
}
dfs(res,s,0,1,"");
return res;
}
public void dfs(List<String> res,String s,int start,int pos,String tem){
if((start > (s.length() -1)) && (pos < 4)){
return;
}
if(pos == 4){
if(isvalid(s.substring(start))){
tem = tem + "." + s.substring(start);
res.add(tem);
return;
}
}
for(int i = 1;i <= 3;i++){
if((start + i) >= s.length()){
return;
}
if(isvalid(s.substring(start,start + i))){
if(pos != 1){
tem = tem + "." + s.substring(start,start + i);
dfs(res,s,start + i,pos + 1,tem);
tem = tem.substring(0,tem.length()-i-1);
}else{
tem = tem + s.substring(start,start + i);
dfs(res,s,start + i,pos + 1,tem);
tem = "";
}
}
}
}
public boolean isvalid(String num){
if(null == num || num.length() <= 0 ){
return false;
}
Long a = Long.parseLong(num);
if(num.length()==1 && a>=0 && a<=9) return true;
if(num.length()==2 && !num.startsWith("0") && a>=10 && a<=99) return true;
if(num.length()==3 && !num.startsWith("0") && a>=100 && a<=255) return true;
return false;
}
}
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