<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<string> possibleIps{};
        string ans{};
        recursiveSearch(s, possibleIps, ans, 0, 0);
        return possibleIps;
    }
private:
    void recursiveSearch(const string& s, vector<string>& ret, string& ans, size_t index, size_t depth) {
        if (depth == 4) {
            if (index == s.size()) {
                ret.push_back(ans);
            }
        }

        string tmp{ans};
        if (depth != 0) {
            ans.push_back('.');
        }

        if (s[index] == '0') {
            ans.push_back('0');
            recursiveSearch(s, ret, ans, index + 1, depth+1);
        } else {
            string part{};
            for (size_t i = index; i < min(s.size(), index+ 3); i++) {
                char num = s[i];
                part+=num;
                if (isValid(part)) {
                    ans.push_back(num);
                    recursiveSearch(s, ret, ans, i+1, depth+1);
                }
                else {
                    break;
                }
            }
        }
        ans = tmp;
    }

    bool isValid(string& tmp) {
        return stoi(tmp) <= 255;
    }
};
15410