Add getting around recursion limit vid

Author: jamesmurphy-mc

README.md

@@ -12,6 +12,7 @@ James and his team are available for consulting, contracting, code reviews, and
 
 | N | Code | Video | 
 | -- | --- |--- |
+| 113 | [src](videos/113_getting_rid_of_recursion) | [Getting around the recursion limit](https://youtu.be/1dUpHL5Yg8E) |
 | 112 | [src](videos/112_python_name_mangling) | [Every Python dev falls for this (name mangling)](https://youtu.be/0hrEaA3N3lk) |
 | 111 | [src](videos/111_python_closures) | [Functions within functions, closures, and variable scopes in Python](https://youtu.be/jXugs4B3lwU) |
 | 110 | [src](videos/110_rvo_and_copy_elision) | [Return Value Optimization and Copy Elision in C++](https://youtu.be/HNYOx-Vh_VA) |

videos/113_getting_rid_of_recursion/tree_traversal.py

@@ -0,0 +1,118 @@
+from __future__ import annotations
+
+
+class Node:
+    def __init__(self, *children: Node, data=None):
+        self.children = list(children)
+        self.data = data
+
+    def __repr__(self):
+        return f'({self.data})'
+
+
+# initial recursive implementation
+def print_parent_then_children(node: Node):
+    print(node)
+    for child in node.children:
+        print_parent_then_children(child)
+
+
+# first try using stack
+def print_parent_then_children(node: Node):
+    stack = [node]
+
+    while stack:
+        node = stack.pop()
+        print(node)
+        for child in node.children:
+            stack.append(child)
+
+
+# fixed issue with order of pushing onto stack
+def print_parent_then_children(node: Node):
+    stack = [node]
+
+    while stack:
+        node = stack.pop()
+        print(node)
+        for child in reversed(node.children):
+            stack.append(child)
+
+
+# recursive implementation with max depth
+def print_parent_then_children(node: Node, max_depth=-1):
+    print(node)
+    if max_depth == 0:
+        return
+    for child in node.children:
+        print_parent_then_children(child, max_depth - 1)
+
+
+# stack version with max depth
+def print_parent_then_children(node: Node, max_depth=-1):
+    stack = [(node, max_depth)]
+    while stack:
+        node, max_depth = stack.pop()
+        print(node)
+        if max_depth == 0:
+            continue
+        for child in reversed(node.children):
+            stack.append((child, max_depth - 1))
+
+
+# factor out the iteration
+def walk_parent_then_children(node: Node, max_depth=-1):
+    stack = [(node, max_depth)]
+    while stack:
+        node, max_depth = stack.pop()
+        yield node
+        if max_depth == 0:
+            continue
+        for child in reversed(node.children):
+            stack.append((child, max_depth - 1))
+
+
+# decoupled implementation
+def print_parent_then_children(node: Node, max_depth=-1):
+    for node in walk_parent_then_children(node, max_depth):
+        print(node)
+
+
+# root -> child 0 -> child 1 -> ...
+def long_tree_example():
+    root = Node(data="root")
+    node = root
+    for n in range(1000):
+        new = Node(data=f"child {n}")
+        node.children.append(new)
+        node = new
+
+    print_parent_then_children(root)
+
+
+#            root
+#    child 0      child 1
+# 0-0  0-1  0-2
+def small_example():
+    root = Node(
+        Node(
+            Node(data="child 0-0"),
+            Node(data="child 0-1"),
+            Node(data="child 0-2"),
+            data="child 0",
+        ),
+        Node(data="child 1"),
+        data="root",
+    )
+
+    print_parent_then_children(root)
+    print(list(walk_parent_then_children(root, max_depth=1)))
+
+
+def main():
+    small_example()
+    long_tree_example()
+
+
+if __name__ == '__main__':
+    main()