<p>A <strong>valid IP address</strong> consists of exactly four integers separated by single dots. Each integer is between <code>0</code> and <code>255</code> (<strong>inclusive</strong>) and cannot have leading zeros.</p>

<ul>
	<li>For example, <code>&quot;0.1.2.201&quot;</code> and <code>&quot;192.168.1.1&quot;</code> are <strong>valid</strong> IP addresses, but <code>&quot;0.011.255.245&quot;</code>, <code>&quot;192.168.1.312&quot;</code> and <code>&quot;192.168@1.1&quot;</code> are <strong>invalid</strong> IP addresses.</li>
</ul>

<p>Given a string <code>s</code> containing only digits, return <em>all possible valid IP addresses that can be formed by inserting dots into </em><code>s</code>. You are <strong>not</strong> allowed to reorder or remove any digits in <code>s</code>. You may return the valid IP addresses in <strong>any</strong> order.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;25525511135&quot;
<strong>Output:</strong> [&quot;255.255.11.135&quot;,&quot;255.255.111.35&quot;]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;0000&quot;
<strong>Output:</strong> [&quot;0.0.0.0&quot;]
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;101023&quot;
<strong>Output:</strong> [&quot;1.0.10.23&quot;,&quot;1.0.102.3&quot;,&quot;10.1.0.23&quot;,&quot;10.10.2.3&quot;,&quot;101.0.2.3&quot;]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 20</code></li>
	<li><code>s</code> consists of digits only.</li>
</ul>

class Solution {
public:
   bool isvalid(string s){
    if(s.length() > 1 && s[0]=='0'){
        return false;
    }
     int val=stoi(s);
    return val>=0 && val<=255;
   } 

   void f( vector<string>&res,string &s,string curr,int ind,int part){
    int n=s.length();
    if(ind==s.length() && part==4){
        res.push_back(curr.substr(0,curr.length()-1));
        return ;
    }
    if(ind+1<=n){
        f(res,s,curr+s.substr(ind,1)+".",ind+1,part+1);
    }
     if(ind+2<=n && isvalid(s.substr(ind,2))){
        f(res,s,curr+s.substr(ind,2)+".",ind+2,part+1);
    }
     if(ind+3<=n && isvalid(s.substr(ind,3))){
        f(res,s,curr+s.substr(ind,3)+".",ind+3,part+1);
    }

   }

    vector<string> restoreIpAddresses(string s) {
        vector<string>res;
        string ds="";
        int n=s.length();
        if(n>12){
            return res;
        }
        f(res,s,ds,0,0);
        return res;
    }
};
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