<p>Given an integer array of even length <code>arr</code>, return <code>true</code><em> if it is possible to reorder </em><code>arr</code><em> such that </em><code>arr[2 * i + 1] = 2 * arr[2 * i]</code><em> for every </em><code>0 &lt;= i &lt; len(arr) / 2</code><em>, or </em><code>false</code><em> otherwise</em>.</p>

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

<pre>
<strong>Input:</strong> arr = [3,1,3,6]
<strong>Output:</strong> false
</pre>

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

<pre>
<strong>Input:</strong> arr = [2,1,2,6]
<strong>Output:</strong> false
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> arr = [4,-2,2,-4]
<strong>Output:</strong> true
<strong>Explanation:</strong> We can take two groups, [-2,-4] and [2,4] to form [-2,-4,2,4] or [2,4,-2,-4].
</pre>

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

<ul>
	<li><code>2 &lt;= arr.length &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>arr.length</code> is even.</li>
	<li><code>-10<sup>5</sup> &lt;= arr[i] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    bool canReorderDoubled(vector<int>& nums) {
        set<int> st1 , st2;
        unordered_map<int,int> mp;
        for(int i = 0; i < nums.size(); ++i){
            if(nums[i] >= 0) st1.insert(nums[i]);
            else st2.insert(nums[i]);
            mp[nums[i]]++;
        }
        for(auto val : st1){
            int cnt1 = mp[val];
            if(cnt1 == 0) continue;
            int findVal = val * 2;
            if(mp.find(findVal) == mp.end()) return false;
            mp[findVal] -= cnt1;
            if(mp[findVal] < 0) return false;
        }
        for(auto it = st2.rbegin(); it != st2.rend(); ++it){
            int val = *it;
            int cnt1 = mp[val];
            if(cnt1 == 0) continue;
            int findVal = val * 2;
            if(mp.find(findVal) == mp.end()) return false;
            mp[findVal] -= cnt1;
            if(mp[findVal] < 0) return false;
        }
        return true;
    }
};
62200