<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 Solution {
public:

    int build(vector<int> &sg, int nd,int l,int r,int mark){

        if(l>r){
            return 0;
        }

        if(mark<l||mark>r){
            return sg[nd];
        }

        if(l==r&&l==mark){
            sg[nd]++;
            return sg[nd];
        }

        int mid=(l+r)/2;

        int a=build(sg,2*nd+1,l,mid,mark);

        int b=build(sg,2*nd+2,mid+1,r,mark);

        return sg[nd]=a+b;

    }


    int find(vector<int> &sg, int nd,int l,int r,int mark){
        if(l>r){
            return 0;
        }

        if(mark<l){
            return 0;
        }

        if(mark>r){
            return sg[nd];
        }

        if(l==r){
            return sg[nd];
        }

        int mid=(l+r)/2;
        
        int a=find(sg,2*nd+1,l,mid,mark);

        int b=find(sg,2*nd+2,mid+1,r,mark);

        return a+b;

    }

    vector<int> countSmaller(vector<int>& s) {

        int n=s.size();
        vector<int> sg(4*1e5+1,0);
        vector<int>ans;

        for(int i=n-1;i>=0;i--){
            build(sg,0,0,1e5,s[i]+1e4);

            int t=find(sg,0,0,1e5,s[i]+1e4-1);

            ans.push_back(t);
        }

        reverse(ans.begin(),ans.end());

        return ans;


        
    }
};
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