<p>Given an integer array <code>nums</code>, return <em>the number of <strong>reverse pairs</strong> in the array</em>.</p>

<p>A <strong>reverse pair</strong> is a pair <code>(i, j)</code> where:</p>

<ul>
	<li><code>0 &lt;= i &lt; j &lt; nums.length</code> and</li>
	<li><code>nums[i] &gt; 2 * nums[j]</code>.</li>
</ul>

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

<pre>
<strong>Input:</strong> nums = [1,3,2,3,1]
<strong>Output:</strong> 2
<strong>Explanation:</strong> The reverse pairs are:
(1, 4) --&gt; nums[1] = 3, nums[4] = 1, 3 &gt; 2 * 1
(3, 4) --&gt; nums[3] = 3, nums[4] = 1, 3 &gt; 2 * 1
</pre>

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

<pre>
<strong>Input:</strong> nums = [2,4,3,5,1]
<strong>Output:</strong> 3
<strong>Explanation:</strong> The reverse pairs are:
(1, 4) --&gt; nums[1] = 4, nums[4] = 1, 4 &gt; 2 * 1
(2, 4) --&gt; nums[2] = 3, nums[4] = 1, 3 &gt; 2 * 1
(3, 4) --&gt; nums[3] = 5, nums[4] = 1, 5 &gt; 2 * 1
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>-2<sup>31</sup> &lt;= nums[i] &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

class Solution {
public:
    vector<int> t;
    void update(int idx,int l,int r,int val)
    {
        if(l>val || r<val)
            return;
        if(l==r){
            t[idx]++;
            return;
        }
        int mid=(l+r)/2;
        update(2*idx,l,mid,val);
        update(2*idx+1,mid+1,r,val);
        t[idx]=t[2*idx]+t[2*idx+1];
    }
    int query(int idx,int l,int r,int lq)
    {
        if(r<lq)
            return 0;
        if(lq<=l)
            return t[idx];
        int mid=(l+r)/2;
        return query(2*idx,l,mid,lq)+query(2*idx+1,mid+1,r,lq);
    }
    int reversePairs(vector<int>& nums) {
        map<long long,int> Map;
        for(auto &x : nums){
            Map[x];
            Map[2ll*x];
        }
        // 1 2 3 4 6
        int cnt=0;
        for(auto &x : Map)
            x.second=cnt++;
        t=vector<int> (4*cnt+10);
        int ans=0;
        for(int i=0;i<nums.size();i++){
            ans+=query(1,0,cnt,Map[2ll*nums[i]]+1);
            cout<<ans<<" ";
            update(1,0,cnt,Map[nums[i]]);
        }
        return ans;
    }
};
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