<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 valid(string& curr){
        string temp = "";
        for (int i=0 ; i<curr.size() ; i++){
            if ((curr[i] < 48 || curr[i] > 57 ) && (curr[i] != '.')) return 0;
            if (curr[i] == '.'){
                if (temp.size() > 3) return 0;
                int val = stoi(temp);
                if (val > 255) return 0;
                if (temp.size() >= 2 && temp[0] == '0') return 0;
                temp = ""; 
            }
            else{
                temp+= curr[i];
            }
        }
        if (temp.size() > 3) return 0;
        int val = stoi(temp);
        if (val > 255) return 0;
        if (temp.size() >= 2 && temp[0] == '0') return 0;
        return 1;
    }

    void func(vector <string> &ans , string &curr , string &s , int idx , int dot){
        if (idx >= curr.size()-1){
            if (dot == 3 && valid(curr)) ans.push_back(curr);
            return;
        }
        if (dot > 3) return;
        curr = curr.substr(0 , idx+1) + "." + curr.substr(idx+1 , curr.size() - 1 - idx);
        func(ans , curr , s , idx+2 , dot+1);
        curr = curr.substr(0 , idx+1) + curr.substr(idx+2 , curr.size()-2-idx);

        func(ans , curr , s , idx+1 , dot);

    }

    vector<string> restoreIpAddresses(string s) {
        if (s.size() > 12) return {};
        vector <string> ans;
        string curr = s;
        func(ans , curr , s , 0 , 0);
        return ans;
    }
};
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