<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 valid(string& str,int start,int length){
        return (length==1 || (str[start]!='0' && (length<3 || str.substr(start,length)<="255")));
    }
    void solve(int startIdx,string s,vector<int>&dots,vector<string>&ans){
        int remainingStr=s.length()-startIdx;
        int remainingSeg=4-dots.size();
        if(remainingStr>remainingSeg*3 || remainingStr<remainingSeg)return;
        if(dots.size()==3){
            if(valid(s,startIdx,remainingStr)){
                string temp="";
                int dotPos=0;
                for(auto len:dots){
                    temp+=s.substr(dotPos,len);
                    dotPos+=len;
                    temp+=".";
                }
                temp+=s.substr(startIdx);
                ans.push_back(temp);
            }
            return ;
        }
        for(int curPos=1;curPos<=3&&curPos<=remainingStr;curPos++){
            dots.push_back(curPos);
            if(valid(s,startIdx,curPos)){
                solve(startIdx+curPos,s,dots,ans);
            }
            dots.pop_back();
        }
    }
    vector<string> restoreIpAddresses(string s) {
        vector<int>dots;
        vector<string>ans;
        solve(0,s,dots,ans);
        return ans;
    }
};
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