diff --git a/01-tree_successor/cpp/Makefile b/01-tree_successor/cpp/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..9feafbe75fdce9e90992dd6e409d359fea098b3c
--- /dev/null
+++ b/01-tree_successor/cpp/Makefile
@@ -0,0 +1,12 @@
+test: tree_successor_test
+ ./$<
+
+CXXFLAGS=-std=c++11 -O2 -Wall -Wextra -g -Wno-sign-compare
+
+tree_successor_test: tree_successor.h tree_successor_test.cpp test_main.cpp
+ $(CXX) $(CXXFLAGS) $^ -o $@
+
+clean:
+ rm -f tree_successor_test
+
+.PHONY: clean test
diff --git a/01-tree_successor/cpp/test_main.cpp b/01-tree_successor/cpp/test_main.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..3f4aff0785f636b7fd0ea1a15aa69dafe06f290f
--- /dev/null
+++ b/01-tree_successor/cpp/test_main.cpp
@@ -0,0 +1,43 @@
+#include <cstdlib>
+#include <functional>
+#include <iostream>
+#include <string>
+#include <utility>
+#include <vector>
+
+using namespace std;
+
+extern vector<pair<string, function<void()>>> tests;
+
+void expect_failed(const string& message) {
+ cerr << "Test error: " << message << endl;
+ exit(1);
+}
+
+int main(int argc, char* argv[]) {
+ vector<string> required_tests;
+
+ if (argc > 1) {
+ required_tests.assign(argv + 1, argv + argc);
+ } else {
+ for (const auto& test : tests)
+ required_tests.push_back(test.first);
+ }
+
+ for (const auto& required_test : required_tests) {
+ bool found = false;
+ for (const auto& test : tests)
+ if (required_test == test.first) {
+ cerr << "Running test " << required_test << endl;
+ test.second();
+ found = true;
+ break;
+ }
+ if (!found) {
+ cerr << "Unknown test " << required_test << endl;
+ return 1;
+ }
+ }
+
+ return 0;
+}
diff --git a/01-tree_successor/cpp/tree_successor.h b/01-tree_successor/cpp/tree_successor.h
new file mode 100644
index 0000000000000000000000000000000000000000..d1306f6ea2e0fa3af6674da904e72898fe1dcc45
--- /dev/null
+++ b/01-tree_successor/cpp/tree_successor.h
@@ -0,0 +1,73 @@
+// A node of the tree
+class Node {
+ public:
+ int key;
+ Node* left;
+ Node* right;
+ Node* parent;
+
+ // Constructor
+ Node(int key, Node* parent=nullptr) {
+ this->key = key;
+ this->parent = parent;
+ this->left = nullptr;
+ this->right = nullptr;
+ }
+};
+
+// Binary tree
+class Tree {
+ public:
+ // Pointer to root of the tree; nullptr if the tree is empty.
+ Node* root = nullptr;
+
+ // Insert a key into the tree.
+ // If the key is already present, nothing happens.
+ void insert(int key) {
+ if (!root) {
+ root = new Node(key);
+ return;
+ }
+
+ Node* node = root;
+ while (node->key != key) {
+ if (key < node->key) {
+ if (!node->left)
+ node->left = new Node(key, node);
+ node = node->left;
+ } else {
+ if (!node->right)
+ node->right = new Node(key, node);
+ node = node->right;
+ }
+ }
+ }
+
+ // Return successor of the given node.
+ //
+ // The successor of a node is the node with the next higher key.
+ // Return nullptr if there is no such node.
+ // If the argument is nullptr, return the node with the smallest key.
+ Node* successor(Node* node) {
+ // TODO: Implement
+ }
+
+ // Destructor to free all allocated memory.
+ ~Tree() {
+ Node* node = root;
+ while (node) {
+ Node* next;
+ if (node->left) {
+ next = node->left;
+ node->left = nullptr;
+ } else if (node->right) {
+ next = node->right;
+ node->right = nullptr;
+ } else {
+ next = node->parent;
+ delete node;
+ }
+ node = next;
+ }
+ }
+};
diff --git a/01-tree_successor/cpp/tree_successor_test.cpp b/01-tree_successor/cpp/tree_successor_test.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..8b794af982614769d379d77b4f896f5803bdffec
--- /dev/null
+++ b/01-tree_successor/cpp/tree_successor_test.cpp
@@ -0,0 +1,54 @@
+#include <algorithm>
+#include <functional>
+#include <cstdint>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "tree_successor.h"
+
+using namespace std;
+
+// If the condition is not true, report an error and halt.
+#define EXPECT(condition, message) do { if (!(condition)) expect_failed(message); } while (0)
+void expect_failed(const string& message);
+
+void test(const vector<int>& sequence) {
+ Tree tree;
+ for (const auto& element : sequence)
+ tree.insert(element);
+
+ vector<int> sorted_sequence(sequence);
+ sort(sorted_sequence.begin(), sorted_sequence.end());
+
+ Node* node = tree.successor(nullptr);
+ for (const auto& element : sorted_sequence) {
+ EXPECT(node, "Expected successor " + to_string(element) + ", got nullptr");
+ EXPECT(node->key == element,
+ "Expected successor " + to_string(element) + ", got " + to_string(node->key));
+ node = tree.successor(node);
+ }
+ EXPECT(!node, "Expected no successor, got " + to_string(node->key));
+}
+
+vector<pair<string, function<void()>>> tests = {
+ {"right_path", []
+ { vector<int> numbers;
+ for (int i = 0; i < 10000; i++) numbers.push_back((int)(7.13*i));
+ test(numbers);
+ }
+ },
+ {"left_path", []
+ { vector<int> numbers;
+ for (int i = 9999; i >= 0; i--) numbers.push_back((int)(7.13*i));
+ test(numbers);
+ }
+ },
+ {"random_tree", []
+ { vector<int> numbers = {997};
+ for (int i = 2; i < 199999; i++)
+ numbers.push_back((numbers.back() * int64_t(997)) % 199999);
+ test(numbers);
+ }
+ },
+};
diff --git a/01-tree_successor/python/tree_successor.py b/01-tree_successor/python/tree_successor.py
new file mode 100644
index 0000000000000000000000000000000000000000..d0377ab6cf0725f68a0f4542a97b78aadc1fcfa7
--- /dev/null
+++ b/01-tree_successor/python/tree_successor.py
@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+
+class Node:
+ """Node in a binary tree `Tree`"""
+
+ def __init__(self, key, left=None, right=None, parent=None):
+ self.key = key
+ self.left = left
+ self.right = right
+ self.parent = parent
+
+class Tree:
+ """A simple binary search tree"""
+
+ def __init__(self, root=None):
+ self.root = root
+
+ def insert(self, key):
+ """Insert key into the tree.
+
+ If the key is already present, do nothing.
+ """
+ if self.root is None:
+ self.root = Node(key)
+ return
+
+ node = self.root
+ while node.key != key:
+ if key < node.key:
+ if node.left is None:
+ node.left = Node(key, parent=node)
+ node = node.left
+ else:
+ if node.right is None:
+ node.right = Node(key, parent=node)
+ node = node.right
+
+ def successor(self, node=None):
+ """Return successor of the given node.
+
+ The successor of a node is the node with the next greater key.
+ Return None if there is no such node.
+ If the argument is None, return the node with the smallest key.
+ """
+ # TODO: Implement
+ raise NotImplementedError
diff --git a/01-tree_successor/python/tree_successor_test.py b/01-tree_successor/python/tree_successor_test.py
new file mode 100644
index 0000000000000000000000000000000000000000..41d691423275ead31f514068f9e27913f195c871
--- /dev/null
+++ b/01-tree_successor/python/tree_successor_test.py
@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+import sys
+
+import tree_successor
+
+def test_sequence(sequence):
+ tree = tree_successor.Tree()
+ for i in sequence: tree.insert(i)
+
+ node = tree.successor(None)
+ for element in sorted(sequence):
+ assert node is not None, "Expected successor {}, got None".format(element)
+ assert node.key == element, "Expected successor {}, got {}".format(element, node.key)
+ node = tree.successor(node)
+ assert node is None, "Expected no successor, got {}".format(node.key)
+
+def gen_increasing_seq():
+ return [int(7.13*i) for i in range(10000)]
+
+tests = [
+ ("right_path", lambda: test_sequence(gen_increasing_seq())),
+ ("left_path", lambda: test_sequence(list(reversed(gen_increasing_seq())))),
+ ("random_tree", lambda: test_sequence([pow(997, i, 199999) for i in range(1, 199999)])),
+]
+
+if __name__ == "__main__":
+ for required_test in sys.argv[1:] or [name for name, _ in tests]:
+ for name, test in tests:
+ if name == required_test:
+ print("Running test {}".format(name), file=sys.stderr)
+ test()
+ break
+ else:
+ raise ValueError("Unknown test {}".format(name))
diff --git a/01-tree_successor/task.md b/01-tree_successor/task.md
new file mode 100644
index 0000000000000000000000000000000000000000..eb2187e4730cf2624feb5b43db16c564dcb97fed
--- /dev/null
+++ b/01-tree_successor/task.md
@@ -0,0 +1,13 @@
+Given an implementation of a simple binary search tree including parent
+pointers, implement a `successor` method. The methods is given a node
+and it should return another node of the tree with the next higher key
+(i.e., the smallest of keys which are greater than the given one).
+
+- If there is no such node, it should return a null pointer.
+- The given node can also be a null pointer, in which case the method should
+ return the smallest node in the tree.
+
+You can expect that `successor` method is never called on an empty tree.
+
+You should submit the file `tree_successor.*` (but not the
+`tree_successor_test.*`).