<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:
    void helper(string s,int index, string res,int count,vector<string> &ans)
    {
        if(index>= s.length())
        {
            if(count==4){
                res = res.substr(0,res.length()-1);
                ans.push_back(res);
            }
            return;
        }
       
        if(s[index] == '0')
        {
            helper(s,index+1,res+"0.",count+1,ans);
        }
        else
        {
            helper(s,index+1,res+s[index]+".",count+1,ans);
            if(index+2<=s.length())
                helper(s,index+2,res+s[index]+s[index+1]+".",count+1,ans);
            if(index+3<=s.length() && stoi(s.substr(index,3))<=255)
                helper(s,index+3,res+s[index]+s[index+1]+s[index+2]+".",count+1,ans);
        }
        return;
    }
    
    vector<string> restoreIpAddresses(string s) {
        vector<string> ans;
        if(s.length()<4 || s.length()>12)
            return ans;
        
        helper(s,0,"",0,ans);
        return ans;
    }
};
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