<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) {
        vector<vector<string>> r;
        vector<string> current;
        backtrack(s, 0, current, r);
        vector<string> result;
        for(int i=0; i<r.size(); i++){
            if(r[i].size()==4){
                string temp="";
                for(int j=0; j<4; j++){
                    temp += r[i][j];
                    if (j < 3) temp += ".";
                }
                result.push_back(temp);
            }
        }
        return result;
    }

private:
    void backtrack(const string& s, int start, vector<string>& current, vector<vector<string>>& result) {
        if (start == s.length()) {
            result.push_back(current);
            return;
        }
        
        for (int end = start; end < min(start + 3, static_cast<int>(s.length())); end++) {
            string segment = s.substr(start, end - start + 1);
            if (isValidSegment(segment)) {
                current.push_back(segment);
                backtrack(s, end + 1, current, result);
                current.pop_back();
            }
        }
    }

    bool isValidSegment(const string& s) {
        if (s.empty() || s.length() > 3 || (s[0] == '0' && s.length() > 1)) return false;
        int num = stoi(s);
        return num >= 0 && num <= 255;
    }
};
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