<p>Given an integer array <code>nums</code>, return<em> an integer array </em><code>counts</code><em> where </em><code>counts[i]</code><em> is the number of smaller elements to the right of </em><code>nums[i]</code>.</p>

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

<pre>
<strong>Input:</strong> nums = [5,2,6,1]
<strong>Output:</strong> [2,1,1,0]
<strong>Explanation:</strong>
To the right of 5 there are <b>2</b> smaller elements (2 and 1).
To the right of 2 there is only <b>1</b> smaller element (1).
To the right of 6 there is <b>1</b> smaller element (1).
To the right of 1 there is <b>0</b> smaller element.
</pre>

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

<pre>
<strong>Input:</strong> nums = [-1]
<strong>Output:</strong> [0]
</pre>

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

<pre>
<strong>Input:</strong> nums = [-1,-1]
<strong>Output:</strong> [0,0]
</pre>

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

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

class SegmentTree{
private:
    vector<long long int> seg;
    int n;
    void update(int pos, int value, long long int idx, int start, int end){
        if(start==end){
            seg[idx]+=value;
            return;
        }
        int midd=(start+end)/2;
        if(pos<=midd) update(pos,value,2*idx+1,start,midd);
        else update(pos,value,2*idx+2,midd+1,end);
        seg[idx]=seg[2*idx+1]+seg[2*idx+2];
    }
    int query(int left, int right, long long int idx, int start, int end){
        if(right<start || left>end) return 0;
        if(left<=start && end<=right) return seg[idx];
        int midd=(start+end)/2;
        int left_val=query(left,right,2*idx+1,start,midd);
        int right_val=query(left,right,2*idx+2,midd+1,end);
        return left_val+right_val;
    }
public:
    SegmentTree(int size){
        n=size;
        seg.resize(4*n,0);
    }
    void update(int index, int value){
        update(index,value,0,0,n-1);
    }
    long long int query(int left, int right){
        return query(left,right,0,0,n-1);
    }
};
class Solution {
public:
    vector<int> countSmaller(vector<int>& nums) {
        int n=nums.size();
        int offset=10000;
        int maxx=20000;
        SegmentTree tree(maxx+1);
        vector<int> ans(n,0);
        for(int i=n-1;i>=0;i--){
            int curr=nums[i]+offset;
            ans[i]=tree.query(0,curr-1);
            tree.update(curr,1);
        }
        return ans;
    }
};
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