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// Call divide(arr, 0, n-1) in the main function
int divide(vector<int> &arr, int l, int r)
{
    if(l >= r)
        return 0;
 
    int mid = (l+r)/2;
    int x = divide(arr, l, mid);
    int y = divide(arr, mid+1, r);
 
    vector<int> ans;
    int a=l, b = mid+1;
    int tmp = 0;
    while (a <= mid && b <= r)
    {
        if (arr[a] <= arr[b])
            ans.push_back(arr[a++]);
        else
        {
            ans.push_back(arr[b++]);
            tmp += (mid-a+1);
        }
    }
 
    while (a <= mid)
    {
        ans.push_back(arr[a++]);
    }
 
    while (b <= r)
    {
        ans.push_back(arr[b++]);
    }
 
    for(int i=0; i<(r-l+1); i++)
    {
        arr[i+l] = ans[i];
    }
 
    return x+y+tmp;
}

prog.cpp:2:12: error: ‘vector’ was not declared in this scope
 int divide(vector<int> &arr, int l, int r)
            ^~~~~~
prog.cpp:2:19: error: expected primary-expression before ‘int’
 int divide(vector<int> &arr, int l, int r)
                   ^~~
prog.cpp:2:30: error: expected primary-expression before ‘int’
 int divide(vector<int> &arr, int l, int r)
                              ^~~
prog.cpp:2:37: error: expected primary-expression before ‘int’
 int divide(vector<int> &arr, int l, int r)
                                     ^~~
prog.cpp:2:42: error: expression list treated as compound expression in initializer [-fpermissive]
 int divide(vector<int> &arr, int l, int r)
                                          ^

Standard output is empty