Sorting books

#include <algorithm>
#include <iostream>
#include <vector>
 
 
 
long long merge(int *dst, int *src, int left, int middle, int end){
  long long numSwaps=0;
  int i = left, j=middle;
  for (int k = left; k<end; k++){
    if (i<middle && (j>=end || src[i]<=src[j])){
      dst[k] = src[i];
      i++;
    } else {
      numSwaps+=middle-i;
      dst[k] = src[j];
      j++;
    }
  }
  return numSwaps;
}
 
 
long long mergeSort(int n, int *data) {
  
  std::vector<int> temp(data, data+n);
 
 
  int *A = data, *B = temp.data();
  long long numSwaps = 0;
  for (int width = 1; width<n; width*=2){
    for (int i = 0; i < n; i +=2 * width){
      int left = i, middle = std::min(i+width,n), end = std::min(i+2*width,n);
      numSwaps+=merge(A, B, left,middle,end);
    }
    std::swap(A,B);
  }
 
  return numSwaps;
}
 
 
 
int main(){
  int n;
  std::cin>>n;
  std::vector<int> vals(n);
  for (int i = 0; i<n; ++i){
    std::cin >> vals[i];
  }
 
  long long numSwaps = mergeSort(n, vals.data());
 
  std::cout << numSwaps << "\n";
}

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