<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 validate(string x){
        cout << x << endl;
        int start = 0, end;
        for(int i = 0; i < 4; i++){
            end = x.find('.',start);
            if (x.substr(start, end-start).size() == 0) return false;
            if (x[start] == '0' && x.substr(start, end-start).size() != 1) return false;
            
            if (stoll(x.substr(start, end-start))<0 || stoll(x.substr(start, end-start))>255){
                return false;
            }
            start = end + 1;
        }
        return true;
    }
    void solve(string &s, vector<string>&ans, string temp, int i, int k){
        if(k == 3){
            if (validate(temp)) {
                ans.push_back(temp);
            }
            return;
        }
        if (i == temp.size()) return;

        string t = temp.substr(0, i) + "." + temp.substr(i);
        solve(s, ans, t, i + 2, k + 1);
        solve(s, ans, temp, i + 1, k);
    }
    vector<string> restoreIpAddresses(string s) {
        vector<string>ans;
        solve(s,ans, s, 1, 0);
        return ans;
    }
};
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