<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 isValid(string s){
        int num1,num2,num3,num4, n = s.length();
        char d1,d2,d3;
        stringstream ss(s);
        string str;
        // check for leading zeroes
        for(int i=0; i<n; i++){
            if(s[i]=='.'){
                if(str=="") return false;
                if(str.length()>1 && str[0]=='0') return false;
                str = "";
            }
            else {
                str += s[i];
            }
        }
        if(str=="" || (str.length()>1 && str[0]=='0')) return false;
        // check if the numbers are in range
        if(ss >> num1 >> d1 >> num2 >> d2 >> num3 >> d3 >> num4) {
            if(d1 == '.' && d3 == '.' && d3 == '.'){
                if(num1>=0 && num1<=255 && num2>=0 && 
                    num2<=255 && num3>=0 && num3<=255 && 
                    num4>=0 && num4<=255){
                    return true;
                }
            }
        }
        return false;
    }
    void solve(int i, int n, string cur, int dot, string s, vector<string>& res){
        if(i==n && dot==3 && isValid(cur)){
            res.push_back(cur);
            return;
        }
        if(i==n){
            return;
        }
        if(i>0 && dot<3 && cur.back()!='.'){
            solve(i,n,cur+'.',dot+1,s,res);
        }
        solve(i+1,n,cur+s[i],dot,s,res);
    }
    vector<string> restoreIpAddresses(string s) {
        string cur;
        vector<string> res;
        solve(0,s.length(),cur,0,s,res);
        return res;
    }
};
23134