diff --git a/map/CMakeLists.txt b/map/CMakeLists.txt
index ec37679..203fc8f 100644
--- a/map/CMakeLists.txt
+++ b/map/CMakeLists.txt
@@ -31,4 +31,5 @@ add_test(NAME mp_five COMMAND sh -c "${CMAKE_CURRENT_BINARY_DIR}/mp_five >/tmp/f
 add_test(NAME mp_five_mem COMMAND sh -c "${CMAKE_CURRENT_BINARY_DIR}/mp_five_mem >/tmp/five_mem_out.txt\
         && diff -u ${CMAKE_CURRENT_SOURCE_DIR}/data/five.memcheck/answer.txt /tmp/five_mem_out.txt>/tmp/five_mem_diff.txt")
 add_subdirectory(test)
-add_executable(subtask1 ${CMAKE_CURRENT_SOURCE_DIR}/src/subtask1.cpp)
\ No newline at end of file
+add_executable(subtask1 ${CMAKE_CURRENT_SOURCE_DIR}/src/subtask1.cpp)
+add_executable(subtask2 ${CMAKE_CURRENT_SOURCE_DIR}/src/subtask2.cpp)
\ No newline at end of file
diff --git a/map/src/map.hpp b/map/src/map.hpp
index 43c5eb1..59366a0 100644
--- a/map/src/map.hpp
+++ b/map/src/map.hpp
@@ -653,6 +653,7 @@ class map {
     while (tmp->left != nullptr) tmp = tmp->left;
     return iterator(tmp, this);
   }
+  const_iterator begin() const { return cbegin(); }
   const_iterator cbegin() const {
     if (tree_root == nullptr) return const_iterator(nullptr, this);
     RedBlackTreeNodeType *tmp = tree_root;
@@ -664,6 +665,7 @@ class map {
    * in fact, it returns past-the-end.
    */
   iterator end() { return iterator(nullptr, this); }
+  const_iterator end() const { return cend(); }
   const_iterator cend() const { return const_iterator(nullptr, this); }
   /**
    * checks whether the container is empty
diff --git a/map/src/subtask1.hpp b/map/src/subtask1.hpp
index c79e92e..bddc45b 100644
--- a/map/src/subtask1.hpp
+++ b/map/src/subtask1.hpp
@@ -1,3 +1,5 @@
+#ifndef SJTU_MAP_SUBTASK1_HPP
+#define SJTU_MAP_SUBTASK1_HPP
 #include <algorithm>
 #include <iterator>
 #include <type_traits>
@@ -29,4 +31,5 @@ void my_sort(_Iter __first, _Iter __last) {
     static_assert(sjtu::is_iterator_v<_Iter>, "Not an iterator.");
 }
 
-}  // namespace sjtu
\ No newline at end of file
+}  // namespace sjtu
+#endif
\ No newline at end of file
diff --git a/map/src/subtask2.cpp b/map/src/subtask2.cpp
new file mode 100644
index 0000000..860475b
--- /dev/null
+++ b/map/src/subtask2.cpp
@@ -0,0 +1,37 @@
+#include "subtask2.hpp"
+#include <iostream>
+#include <map>
+#include <string>
+#include <vector>
+#include "../../vector/src/vector.hpp"
+#include "map.hpp"
+int main() {
+  int v[3][4] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
+  sjtu::print(v);
+  std::cout<<std::endl;
+  std::vector<int> a = {1, 2, 3, 4, 5};
+  sjtu::print(a);
+  std::cout << std::endl;
+  std::vector<std::vector<int>> b = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
+  sjtu::print(b);
+  std::cout<<std::endl;
+  sjtu::vector<int> c;
+  c.push_back(1);
+  c.push_back(2);
+  c.push_back(3);
+  sjtu::print(c);
+  std::cout<<std::endl;
+  std::map<int, std::string> d;
+  d[1] = "Hello";
+  d[2] = "World";
+  sjtu::print(d);
+  std::cout<<std::endl;
+  sjtu::map<int, std::string> e;
+  e[1] = "Hello";
+  e[2] = "World";
+  sjtu::print(e);
+  std::cout<<std::endl;
+  int f[3][3][3] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18};
+  sjtu::print(f);
+  return 0;
+}
\ No newline at end of file
diff --git a/map/src/subtask2.hpp b/map/src/subtask2.hpp
new file mode 100644
index 0000000..d612889
--- /dev/null
+++ b/map/src/subtask2.hpp
@@ -0,0 +1,67 @@
+#ifndef SJTU_MAP_SUBTASK2_HPP
+#define SJTU_MAP_SUBTASK2_HPP
+#include <iostream>
+#include <type_traits>
+#include "utility.hpp"
+namespace sjtu {
+template <typename _Tp>
+static constexpr bool can_be_used_in_cout_v = requires(std::ostream &os, const _Tp &dat) {
+  os << dat;
+};
+template <typename _Tp>
+static constexpr bool is_pair_v = false;
+template <typename _T1, typename _T2>
+static constexpr bool is_pair_v<std::pair<_T1, _T2> > = true;
+template <typename _T1, typename _T2>
+static constexpr bool is_pair_v<sjtu::pair<_T1, _T2> > = true;
+template <typename _Tp>
+static constexpr bool is_container_v = requires(const _Tp &x) {
+  std::begin(x);
+  std::end(x);
+};
+template <typename _Tp>
+static constexpr bool is_container_s_container_v = requires(const _Tp &x) {
+  std::begin(*std::begin(x));
+  std::end(*std::begin(x));
+};
+template <typename _Tp>
+void print(const _Tp &dat, size_t indent_length = 0) {
+  static constexpr bool need_indent = sjtu::is_container_s_container_v<_Tp>;
+  if constexpr (sjtu::can_be_used_in_cout_v<_Tp>) {
+    if constexpr (std::is_bounded_array_v<_Tp>) {
+      for (size_t i = 0; i < indent_length; i++) std::cout << ' ';
+      std::cout << '[';
+      if constexpr (need_indent) std::cout << '\n';
+      for (size_t i = 0; i < std::extent_v<_Tp>; i++) {
+        if (need_indent == false && i) std::cout << ' ';
+        print(dat[i], indent_length + 1);
+        if constexpr (need_indent) std::cout << '\n';
+      }
+      if constexpr (need_indent)
+        for (size_t i = 0; i < indent_length; i++) std::cout << ' ';
+      std::cout << ']';
+    } else
+      std::cout << dat;
+  } else if constexpr (sjtu::is_container_v<_Tp>) {
+    for (size_t i = 0; i < indent_length; i++) std::cout << ' ';
+    std::cout << '[';
+    if constexpr (need_indent) std::cout << '\n';
+    for (auto it = std::begin(dat); it != std::end(dat); it++) {
+      if (need_indent == false && it != std::begin(dat)) std::cout << ' ';
+      print(*it, indent_length + 1);
+      if constexpr (need_indent) std::cout << '\n';
+    }
+    if constexpr (need_indent)
+      for (size_t i = 0; i < indent_length; i++) std::cout << ' ';
+    std::cout << ']';
+  } else if constexpr (sjtu::is_pair_v<_Tp>) {
+    std::cout << '(';
+    print(dat.first, indent_length);
+    std::cout << ',';
+    print(dat.second, indent_length);
+    std::cout << ')';
+  } else
+    static_assert(sjtu::can_be_used_in_cout_v<_Tp>, "Cannot print this type.");
+}
+}  // namespace sjtu
+#endif
\ No newline at end of file
diff --git a/vector/src/vector.hpp b/vector/src/vector.hpp
index 932914d..be66fbf 100644
--- a/vector/src/vector.hpp
+++ b/vector/src/vector.hpp
@@ -348,11 +348,13 @@ class vector {
    * returns an iterator to the beginning.
    */
   iterator begin() { return iterator(this, raw_beg); }
+  const_iterator begin() const { return const_iterator(this, raw_beg); }
   const_iterator cbegin() const { return const_iterator(this, raw_beg); }
   /**
    * returns an iterator to the end.
    */
   iterator end() { return iterator(this, raw_end); }
+  const_iterator end() const { return const_iterator(this, raw_end); }
   const_iterator cend() const { return const_iterator(this, raw_end); }
   /**
    * checks whether the container is empty