<p>Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size <code>groupSize</code>, and consists of <code>groupSize</code> consecutive cards.</p>

<p>Given an integer array <code>hand</code> where <code>hand[i]</code> is the value written on the <code>i<sup>th</sup></code> card and an integer <code>groupSize</code>, return <code>true</code> if she can rearrange the cards, or <code>false</code> otherwise.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> hand = [1,2,3,6,2,3,4,7,8], groupSize = 3
<strong>Output:</strong> true
<strong>Explanation:</strong> Alice&#39;s hand can be rearranged as [1,2,3],[2,3,4],[6,7,8]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> hand = [1,2,3,4,5], groupSize = 4
<strong>Output:</strong> false
<strong>Explanation:</strong> Alice&#39;s hand can not be rearranged into groups of 4.

</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= hand.length &lt;= 10<sup>4</sup></code></li>
	<li><code>0 &lt;= hand[i] &lt;= 10<sup>9</sup></code></li>
	<li><code>1 &lt;= groupSize &lt;= hand.length</code></li>
</ul>

<p>&nbsp;</p>
<p><strong>Note:</strong> This question is the same as 1296: <a href="https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/" target="_blank">https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/</a></p>

class Solution {
public:

    bool exists_range(int start, int end, unordered_map<int,int>& freq){
        std :: cout << start << " " ;
        if(freq.count(start) == 0)
            return false ;
        if(start == end)
        {
            freq[start]-- ;
            if(freq[start] == 0)
                freq.erase(start) ;
            return true ;
        }
        if(exists_range(start+1,end,freq) == false)
            return false ;
        freq[start]-- ;
        if(freq[start] == 0)
                freq.erase(start) ;
        return true ;
    }

    bool isNStraightHand(vector<int>& hand, int groupSize) {
        if(hand.size() % groupSize != 0)
            return false ;
        unordered_map<int,int> freq ;
        for(int& x : hand)
            if(freq.count(x) == 0)
                freq[x] = 1 ;
            else
                freq[x]++ ;
        while(true){
            bool removed = false; 
            for(int& x : hand){
                if(freq.count(x) == 0)
                    continue ;
                if(freq.count(x-1) == 0){
                    if(exists_range(x,x+groupSize-1, freq))
                        removed = true ;
                }
            }
            if(!removed)
                break ;
        }
        for(int& x: hand)
            if(freq[x] != 0)
                return false ;
        return true ;
    }
};
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