<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:
    vector<string> restoreIpAddresses(string s) {
        return solve(s,3);
    }
    vector<string> solve(string s, int num_dot){
        set<string> res;
        if(num_dot==0){
            if(s.size()<=3&&stoi(s)>=0&&stoi(s)<=255){
                if(s.size()==1||(s.size()>1&&s[0]!='0'))res.insert(s);
            }
        }
        else if(num_dot<s.size()){
            for(int i=0;i<s.size()-1;i++){
                for(int j=0;j<=num_dot-1;j++){
                    vector<string> left=solve(s.substr(0,i+1),j);
                    vector<string> right=solve(s.substr(i+1,s.size()-1-i),num_dot-1-j);
                    if(left.size()>0&&right.size()>0){
                        for(int l=0;l<left.size();l++){
                            for(int r=0;r<right.size();r++){
                                res.insert(left[l]+"."+right[r]);
                            }
                        }
                    }
                }
            }
        }
        vector<string> res_v;
        for(set<string>::iterator it=res.begin();it!=res.end();it++){
            res_v.push_back(*it);
        }
        return res_v;
    }
};
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