平衡树

#include <ext/pb_ds/assoc_container.hpp>  // 因为tree定义在这里 所以需要包含这个头文件
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
__gnu_pbds::tree<Key, Mapped, Cmp_Fn = std::less<Key>, Tag = rb_tree_tag,
                 Node_Update = null_tree_node_update,
                 Allocator = std::allocator<char>>

__gnu_pbds::tree<std::pair<int, int>, __gnu_pbds::null_type,
                 std::less<std::pair<int, int>>, __gnu_pbds::rb_tree_tag,
                 __gnu_pbds::tree_order_statistics_node_update>
    trr;

// Common Header Simple over C++11
#include <iostream>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
__gnu_pbds::tree<pair<int, int>, __gnu_pbds::null_type, less<pair<int, int>>,
                 __gnu_pbds::rb_tree_tag,
                 __gnu_pbds::tree_order_statistics_node_update>
    trr;

int main() {
  int cnt = 0;
  trr.insert(make_pair(1, cnt++));
  trr.insert(make_pair(5, cnt++));
  trr.insert(make_pair(4, cnt++));
  trr.insert(make_pair(3, cnt++));
  trr.insert(make_pair(2, cnt++));
  // 树上元素 {{1,0},{2,4},{3,3},{4,2},{5,1}}
  auto it = trr.lower_bound(make_pair(2, 0));
  trr.erase(it);
  // 树上元素 {{1,0},{3,3},{4,2},{5,1}}
  auto it2 = trr.find_by_order(1);
  cout << (*it2).first << endl;
  // 输出排名 0 1 2 3 中的排名 1 的元素的 first:1
  int pos = trr.order_of_key(*it2);
  cout << pos << endl;
  // 输出排名
  decltype(trr) newtr;
  trr.split(*it2, newtr);
  for (auto i = newtr.begin(); i != newtr.end(); ++i) {
    cout << (*i).first << ' ';
  }
  cout << endl;
  // {4,2},{5,1} 被放入新树
  trr.join(newtr);
  for (auto i = trr.begin(); i != trr.end(); ++i) {
    cout << (*i).first << ' ';
  }
  cout << endl;
  cout << newtr.size() << endl;
  // 将 newtr 树并入 trr 树，newtr 树被删除。
  return 0;
}