<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> ans;
    string curr;
    vector<string> split(string s, char ch) {
        vector<string> ans;
        stringstream ss(s);
        string item;
        while (getline(ss, item, '.')) {
            ans.push_back(item);
        }
        return ans;
    }
    bool isvalid(string str) {
        vector<string> ip = split(str, '.');
        if(ip.size()!=4)
        return false;
        for (auto x : ip) {
            long long y = stoll(x);
            if (!(y >= 0 && y <= 255)) {
                return false;
            }
            string temp = to_string(y);
            if (temp != x) {
                return false;
            }
        }
        return true;
    }
    void rec(int level, string& s, int k) {
        if (level == s.length()) {
            if (k != 3) {
                return;
            } else {
                if (isvalid(curr)) {
                    ans.push_back(curr);
                }
                return;
            }
        }
        if (k > 3) {
            return;
        }
        curr.push_back(s[level]);
        rec(level + 1, s, k);
        curr.pop_back();
        if (k < 3) {
            curr.push_back(s[level]);
            curr.push_back('.');
            rec(level + 1, s, k + 1);
            curr.pop_back();
            curr.pop_back();
        }
    }
    vector<string> restoreIpAddresses(string s) {
        ans.clear();
        rec(0, s, 0);
        return ans;
    }
};
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