<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>& arr) {
        map<int, int> hash;
        for (auto n : arr) hash[n]++;

        for (auto [after, times] : hash) {
            if (times > 0) {
                if (after < 0 && after % 2) return false;
                else {
                    int before = after > 0 ? after * 2 : after / 2;
                    if (hash[before] < times) return false;
                    else hash[before] -= times;
                }
            }
        }
        
        // sort(arr.begin(), arr.end());
        
        // int neg = -1, pos = 0;
        // while (pos < arr.size()) {
        //     if (arr[pos] < 0) {neg = pos++;}
        //     else if (arr[pos] == 0) pos++;
        //     else break;
        // }
        // if ((arr.size() - pos) % 2 || (neg + 1) % 2) return false;

        // int cnt;
        // unordered_map<int, int> hash;

        // cnt = (arr.size() - pos) / 2;
        // for (int i = pos; i < arr.size(); i++) {
        //     if (hash[arr[i]] == 0) hash[arr[i] * 2]++;
        //     else {
        //         hash[arr[i]]--;
        //         cnt--;
        //     }
        // }
        // if (cnt) return false;

        // cnt = (neg + 1) / 2;
        // for (int i = neg; i >= 0; i--) {
        //     if (hash[arr[i]] == 0) hash[arr[i] * 2]++;
        //     else {
        //         hash[arr[i]]--;
        //         cnt--;
        //     }
        // }
        // if (cnt) return false;

        return true;
    }
};
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