u01: Add recursive print with cycle detection

u01/main.cpp

@@ -7,6 +7,14 @@ int main(int argc, char **argv) {
   std::cout << *t;
   delete t;
   t = nullptr;
+
+  node *n = new node("foo");
+  n->add_child(new node("bar"));
+  n->get_child(0)->add_child(n);
+  std::cout << n->print_recursive();
+  delete n;
+  n = nullptr;
+
   node *root = new node("root");
   root->add_child(new node("left child"));
   root->add_child(new node("right child"));

u01/node.cpp

@@ -42,6 +42,24 @@ void node::print(std::ostream &str, std::size_t depth) const {
   }
 }
 
+std::string node::print_recursive(std::size_t depth,
+                                  std::set<const node *> visited) const {
+  std::stringstream output;
+  output << std::string(depth, '\t') << get_name();
+  visited.insert(this);
+  for (const node *child : children) {
+    // std::set::contains is only implemented in C++20
+    if (visited.find(child) == visited.end()) {
+      output << std::endl << child->print_recursive(depth + 1, visited);
+    } else {
+      output << " [↝ " << child->get_name() << "]";
+    }
+  }
+  if (depth == 0)
+    output << std::endl;
+  return output.str();
+}
+
 std::ostream &operator<<(std::ostream &os, node &n) {
   n.print(os);
   return os;

u01/node.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <memory>
+#include <set>
 #include <string>
 #include <vector>
 
@@ -14,6 +15,8 @@ public:
   node *get_child(std::size_t i) const;
   void add_child(node *child);
   void print(std::ostream &str, std::size_t depth = 0) const;
+  std::string print_recursive(std::size_t depth = 0,
+                              std::set<const node *> visited = {}) const;
 
 private:
   std::string name;

u01/tests.cpp

@@ -150,3 +150,16 @@ TEST_CASE("Print stream overload") {
 
   REQUIRE(output1.str() == output2.str());
 }
+
+TEST_CASE("Cycle detection") {
+  node *n = new node("foo");
+  n->add_child(new node("bar"));
+  n->get_child(0)->add_child(n);
+
+  std::stringstream output;
+  output << n->print_recursive();
+
+  REQUIRE(output.str() == "foo\n\tbar [↝ foo]\n");
+
+  delete n;
+}