<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:
     vector<string>ans;
    bool isvalid(int prev,int curr,string &s)
    {
        string substr=s.substr(prev,curr-prev+1);
        if((s[prev]=='0'&&prev!=curr)||curr-prev>=3)
         return false;
        int t=stoi(substr);
        if(t>=0&&t<=255)
         return true;
        return false;
    }
    void find(int prev,int curr,string &s,int n,int count,string &str)
    {
        
       if(prev==n&&count==4)
       {
          str.pop_back();
          ans.push_back(str);
          return;
       }

       if(curr>=n)
         return;

       find(prev,curr+1,s,n,count,str);

       if(isvalid(prev,curr,s))
        {
            string ss=str;
            str+=s.substr(prev,curr-prev+1)+".";
            find(curr+1,curr+1,s,n,count+1,str);
            str=ss;
        }
        return;
    }
    vector<string> restoreIpAddresses(string s) {
        int n=s.size();
        ans.clear();
        if(n>12)
         return ans;
        string str="";
        find(0,0,s,n,0,str);
        return ans;

        
    }
};
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