5-11打卡，交换两个list容器的区间的元素

10-6编写一个具有以下原型的函数模板：
template
void exchange (list& 11, list:: iterator pl, list & 12, list::
iterator p2);
该模板用于将l1链表的[p1，l1.end（））区间和l2链表的[p2，l2.end（））区间的内容
交换。在主函数中调用该模板，以测试该模板的正确性。

#include <iostream>
#include <list>
using namespace std;

// function template to exchange the contents of two list segments
template <class T>
void exchange (list<T>& l1, typename list<T>::iterator p1, list<T>& l2, typename list<T>::iterator p2) {
  // swap the elements from p1 to l1.end() with the elements from p2 to l2.end()
  while (p1 != l1.end() && p2 != l2.end()) {
    swap(*p1, *p2);
    p1++;
    p2++;
  }
  // if one list segment is longer than the other, append the remaining elements to the other list
  if (p1 != l1.end()) {
    l2.splice(l2.end(), l1, p1, l1.end());
  }
  else if (p2 != l2.end()) {
    l1.splice(l1.end(), l2, p2, l2.end());
  }
}

// main function to test the template
int main() {
  // create two lists of integers
  list<int> l1 = {1, 2, 3, 4, 5};
  list<int> l2 = {6, 7, 8};

  // print the original lists
  cout << "l1: ";
  for (int x : l1) {
    cout << x << " ";
  }
  cout << endl;
  
  cout << "l2: ";
  for (int x : l2) {
    cout << x << " ";
  }
  cout << endl;

  // get iterators to the second element of each list
  auto p1 = l1.begin();
  p1++;
  auto p2 = l2.begin();
  p2++;

  // call the exchange template function
  exchange(l1, p1, l2, p2);

  // print the modified lists
  cout << "After exchange:" << endl;
  
  cout << "l1: ";
  for (int x : l1) {
    cout << x << " ";
  }
  cout << endl;
  
  cout << "l2: ";
  for (int x : l2) {
    cout << x << " ";
  }
  cout << endl;

  return 0;
}