<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>

//put order array, each element is set to 1
class SegmentTree
{
public:
    SegmentTree(vector<int>& arr) : n(arr.size()) //put order array
    {
        t.resize(4*n);
        maxv.resize(4*n);
        build(arr,1,0,n-1);
    }
    int getGreater(long long val)
    {
        return getGreater(1,0,n-1,val);
    }
    int getGreaterOrEqual(long long val)
    {
        return getGreaterOrEqual(1,0,n-1,val);
    }
    int getLesser(long long val)
    {
        return t[1]-getGreaterOrEqual(val);
    }
    int getLesserOrEqual(long long val)
    {
        return t[1]-getGreater(val);
    }
    void removeElement(int val)
    {
        return removeElement(1,0,n-1,val);
    }
private:
    int getGreater(int v, int tl, int tr, long long val) {
        if (tl==tr) return maxv[v]>val;
        int tm = (tl + tr) / 2;
        return (maxv[v*2]>val)? getGreater(v*2, tl, tm, val) + t[v*2+1] : getGreater(v*2+1, tm+1, tr, val);
    }
    int getGreaterOrEqual(int v, int tl, int tr, long long val) {
        if (tl==tr) return maxv[v]>=val;
        int tm = (tl + tr) / 2;
        return (maxv[v*2]>=val)? getGreater(v*2, tl, tm, val) + t[v*2+1] : getGreater(v*2+1, tm+1, tr, val);
    }
    void removeElement(int v, int tl, int tr, long long val) {
        if (tl == tr)
        {
            t[v] = 0;
            maxv[v] = -1000000000000000;
        }
        else {
            int tm = (tl + tr) / 2;
            if (maxv[v*2] >= val) removeElement(v*2, tl, tm, val);
            else removeElement(v*2+1, tm+1, tr, val);
            t[v] = t[v*2] + t[v*2+1];
            maxv[v] = max(maxv[v*2],maxv[v*2+1]);
        }
    }
    void build(vector<int>& a, int v, int tl, int tr) {
        if (tl == tr) {
            t[v] = 1;
            maxv[v]=a[tl];
        } else {
            int tm = (tl + tr) / 2;
            build(a, v*2, tl, tm);
            build(a, v*2+1, tm+1, tr);
            t[v] = t[v*2] + t[v*2+1];
            maxv[v] = max(maxv[v*2],maxv[v*2+1]);
        }
    }
    int n;
    vector<int> t;
    vector<long long> maxv;
};

class Solution {
public:
    int reversePairs(vector<int>& nums) {
        int sz = nums.size();
        vector<int> v = nums;
        sort(begin(v),end(v));
        SegmentTree st(v);
        int r = 0;
        for(int i=sz-1;i>=0;i--)
        {
            st.removeElement(nums[i]);
            r+=st.getGreater(2LL*nums[i]);
        }
        return r;
    }
};
68550