<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 {
bool valid(string cur) {
    if (cur.size() == 0)return true;
    int index = cur.find(".");
    if (index == -1) {
        if (cur.size() > 3) return false;
        if(cur[0] == '0' && cur.size() > 1) return false;
        if (stoi(cur) >= 0 && stoi(cur) <= 255) return true;
    }
    string cut = cur.substr(0, index);
    if(cut.size() > 3) return false;
    if (cut[0] == '0' && cut.size() > 1) return false;
    if (stoi(cut) < 0 || stoi(cut) > 255) return false;
    if (valid(cur.substr(index + 1))) return true;
    return false;
}

bool isValidString(string s) {
    for (char c : s) {
        if (!isdigit(static_cast<unsigned char>(c))) {
            return false;
        }
    }
    return true;
}

void helper(vector<string>& ans, string s, int dotCount, int index) {
    if (dotCount == 3) {
        if (valid(s)) {
            ans.push_back(s);
        }
        return;
    }
    if (index == s.size()) return;
    helper(ans, s.substr(0, index) + '.' + s.substr(index),dotCount + 1, index + 2);
    helper(ans, s, dotCount, index + 1);

    return;
}
public:
    vector<string> restoreIpAddresses(string s) {
       vector<string> ans;
    if (isValidString(s)) {
        int dotCount = 0;
        int index = 1;
        helper(ans, s, dotCount, index);
        }
        return ans;
    }
};
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