<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 checkvalid(string str){
        int n=str.length();
        if(n==1) return true;
        if(n>3 ||str[0]=='0') return false;
        int value=stoi(str);
        if(value>255) return false;
        return true;
    }
    vector<string> restoreIpAddresses(string s) {
       int n=s.length();
       vector<string> res;
       if(n>12 || n<4) return { };
       else{
         for(int i=1;i<=3;i++){
             for(int j=1;j<=3;j++){
                 for(int k=1;k<=3;k++){
                     if(i+j+k<n && i+j+k>=n-3){
                         string str1=s.substr(0,i);
                         string str2=s.substr(i,j);
                         string str3=s.substr(i+j,k);
                         string str4=s.substr(i+j+k);
                     
                     if(checkvalid(str1) && checkvalid(str2) && checkvalid(str3) && checkvalid(str4)){
                         res.push_back(str1+"."+str2+"."+str3+"."+str4);
                     }
                     }
                 }
             }
         }
       }
       return res;
    }
};
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