<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.size()==1)return true;
        else if(s.size() == 2){
            if(s[0]=='0')return false;
            return true;
        }
        else if(s.size() == 3){
            if(s[0] == '0')return false;
            int num=stoi(s);
            if(num<0 || num>255)return false;
            return true;
        }
        return true;
    }
    void f(int ind,int dot , vector<string>& v,string temp, string& s){
        if(ind == s.size() && dot == 4){
            temp.pop_back();
            v.push_back(temp);
            return ;
        }

        if( ind + 1 <= s.size()){
            f( ind + 1 , dot + 1 , v , temp + s.substr(ind , 1) + '.' , s );
        }

        if( ind + 2 <= s.size() && isvalid(s.substr(ind , 2))){
            f(ind + 2 , dot + 1 , v , temp + s.substr(ind , 2) + '.' , s);
        }

        if(ind + 3 <= s.size() && isvalid(s.substr(ind , 3))){
            f( ind + 3 , dot + 1 , v , temp + s.substr(ind , 3)+ '.' , s);
        } 
    }

    vector<string> restoreIpAddresses(string s) {
        if(s.size()>12)return {};
        vector<string>v;
        string temp;
        f(0 , 0 , v,temp,s);
        return v;
    }
};
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