u01: Add iterative print with cycle detection

u01/node.cpp

@@ -1,5 +1,6 @@
 #include <iostream>
 #include <sstream>
+#include <stack>
 
 #include "node.h"
 
@@ -60,6 +61,36 @@ std::string node::print_recursive(std::size_t depth,
   return output.str();
 }
 
+std::string node::print_iterative() const {
+  std::stringstream output;
+  std::stack<std::pair<const node *, size_t>> stack;
+  stack.push(std::make_pair(this, 0));
+  std::set<const node *> visited = {};
+
+  while (!stack.empty()) {
+    const node *n = nullptr;
+    size_t depth;
+    std::tie(n, depth) = stack.top();
+    stack.pop();
+    if (visited.find(n) == visited.end()) {
+      if (n != this)
+        output << std::endl;
+      output << std::string(depth, '\t') << n->get_name();
+      // Complex iteration (not default vector iteration is necessary,
+      // to achieve the same output as the recursive approach.
+      // Otherwise, the order of the children is reversed (due to LIFO).
+      for (size_t i = n->get_nr_children(); i > 0; i--) {
+        stack.push(std::make_pair(n->get_child(i - 1), depth + 1));
+      }
+    } else {
+      output << " [↝ " << n->get_name() << "]";
+    }
+    visited.insert(n);
+  }
+  output << std::endl;
+  return output.str();
+}
+
 std::ostream &operator<<(std::ostream &os, node &n) {
   n.print(os);
   return os;

u01/node.h

@@ -17,6 +17,7 @@ public:
   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;
+  std::string print_iterative() const;
 
 private:
   std::string name;

u01/tests.cpp

@@ -163,3 +163,32 @@ TEST_CASE("Cycle detection") {
 
   delete n;
 }
+
+TEST_CASE("Cycle detection (iterative)") {
+  node *n = new node("foo");
+  n->add_child(new node("bar"));
+  n->get_child(0)->add_child(n);
+
+  std::stringstream output;
+  output << n->print_iterative();
+
+  REQUIRE(output.str() == "foo\n\tbar [↝ foo]\n");
+
+  delete n;
+}
+
+TEST_CASE("Equivalence of interative and recursive print") {
+  node *n = new node();
+  REQUIRE(n->print_recursive() == n->print_iterative());
+  delete n;
+
+  node *r = new node("foo");
+  r->add_child(new node("bar"));
+  r->get_child(0)->add_child(r);
+  REQUIRE(r->print_recursive() == r->print_iterative());
+  delete r;
+
+  node *t = create_complete_tree(2, 4);
+  REQUIRE(t->print_recursive() == t->print_iterative());
+  delete t;
+}