<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:
    void func(vector<vector<int>>::iterator l, vector<vector<int>>::iterator r, vector<int>& vec)
    {
        if(r-l<=1)
            return;
        
        vector<vector<int>>::iterator m = l+(r-l)/2;
        func(l,m,vec);
        func(m,r,vec);
        for(vector<vector<int>>::iterator i = l, j = m; i<m; i++)
        {
            while(j<r && (*i)[0] > (*j)[0])
                j++;
            vec[(*i)[1]]+=j-m;
        }
        inplace_merge(l,m,r);
    }

    vector<int> countSmaller(vector<int>& nums) {
        int n = nums.size();
        vector<int>temp;
        if(n==0)
            return temp;
        
        vector<int>vec(n,0);
        vector<vector<int> >mat(n,vector<int>(2));
        for(int i=0;i<n;i++)
        {
            //mat.push_back(vector<int>({nums[i],i}));
            mat[i][0] = nums[i];
            mat[i][1] = i;
        }

        func(mat.begin(), mat.end(), vec);
        return vec;
    }
};
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