<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:

vector<vector<int> > st;
void build(int i, int lo, int hi, vector<int> &arr){
    if(lo == hi){
        st[i].push_back(arr[lo]);
        return;
    }
    int mid = lo + (hi - lo)/2;
    build(2*i+1, lo, mid, arr);
    build(2*i+2, mid +1 , hi, arr);
    vector<int> v;
    int sz = st[2*i+1].size();
    sz += st[2*i+2].size();
    v.resize(sz);
    merge(st[2*i+1].begin(), st[2*i+1].end(), st[2*i+2].begin(), st[2*i+2].end() ,v.begin());
    st[i] = v;
}
int get (vector<int> &v, int k){
    int xx = lower_bound(v.begin(), v.end(), k) - v.begin();
    return xx;
}

int answer(int i, int lo, int hi , int l, int r, int k){
    if(l> hi or r<lo) return 0;
    if(lo>=l and hi <= r) return get(st[i] , k);

    int mid = lo + (hi-lo)/2;
    int left = answer(2*i+1, lo, mid, l,r,k);
    int right = answer(2*i+2, mid+1, hi, l, r, k);
    return left + right;
}


    vector<int> countSmaller(vector<int>& nums) {
        int n = nums.size();
        st.resize(4*n , vector<int> ());
        build(0,0,n-1, nums);

        vector<int> ans;

        for(int i = 0; i<n; i++){
            int l = i+1; int r = n-1;
            int k = nums[i];
            int xx=  answer(0,0, n-1, l,r,k);
            ans.push_back(xx);
        }
        return ans;
    }
};
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