From 84161ab2edb057cc5f796cab8044f61ba431d229 Mon Sep 17 00:00:00 2001
From: Abhinav Sarkar <abhinav@abhinavsarkar.net>
Date: Wed, 17 Jul 2019 10:35:59 +0530
Subject: [PATCH] Adds tree iterators based on CPS defunctionalization

---
 .../abhinavsarkar/algorist/TreeIterators.java | 386 ++++++++++++++++++
 1 file changed, 386 insertions(+)
 create mode 100644 src/main/java/net/abhinavsarkar/algorist/TreeIterators.java

diff --git a/src/main/java/net/abhinavsarkar/algorist/TreeIterators.java b/src/main/java/net/abhinavsarkar/algorist/TreeIterators.java
new file mode 100644
index 0000000..68a124a
--- /dev/null
+++ b/src/main/java/net/abhinavsarkar/algorist/TreeIterators.java
@@ -0,0 +1,386 @@
+package net.abhinavsarkar.algorist;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.function.Consumer;
+
+class TreeIerators {
+    public static void main(String[] args) {
+        Tree<String> tree =
+                new Tree<>(new Tree<>(new Tree<>(null, "x", null), "a", null),
+                        "b",
+                        new Tree<>(new Tree<>(null, "o", null), "c", new Tree<>(null, "r", null)));
+
+        // InOrderIterator
+        InOrderIterator.iterateRecursive(tree, System.out::print);
+        System.out.println("\tInOrderIterator.iterateRecursive");
+
+
+        InOrderIterator.iterateCPS(tree, System.out::print, () -> {});
+        System.out.println("\tInOrderIterator.iterateCPS");
+
+
+        InOrderIterator.iterateDefCPS(tree, System.out::print, null);
+        System.out.println("\tInOrderIterator.iterateDefCPS");
+
+        InOrderIterator.iterate(tree, System.out::print, null);
+        System.out.println("\tInOrderIterator.iterate");
+
+        InOrderIterator<String> inOrderIterator = new InOrderIterator<>(tree);
+        while (inOrderIterator.hasNext()) {
+            System.out.print(inOrderIterator.next());
+        }
+        System.out.println("\tInOrderIterator");
+        System.out.println();
+
+        // PreOrderIterator
+        PreOrderIterator.iterateRecursive(tree, System.out::print);
+        System.out.println("\tPreOrderIterator.iterateRecursive");
+
+        PreOrderIterator.iterateCPS(tree, System.out::print, () -> {});
+        System.out.println("\tPreOrderIterator.iterateCPS");
+
+        PreOrderIterator.iterateDefCPS(tree, System.out::print, null);
+        System.out.println("\tPreOrderIterator.iterateDefCPS");
+
+        PreOrderIterator.iterate(tree, System.out::print, null);
+        System.out.println("\tPreOrderIterator.iterate");
+
+        PreOrderIterator<String> preOrderIterator = new PreOrderIterator<>(tree);
+        while (preOrderIterator.hasNext()) {
+            System.out.print(preOrderIterator.next());
+        }
+        System.out.println("\tPreOrderIterator");
+        System.out.println();
+
+        PostOrderIterator.iterateRecursive(tree, System.out::print);
+        System.out.println("\tPostOrderIterator.iterateRecursive");
+
+        // PostOrderIterator
+        PostOrderIterator.iterateCPS(tree, System.out::print, () -> {});
+        System.out.println("\tPostOrderIterator.iterateCPS");
+
+        PostOrderIterator.iterateDefCPS(tree, System.out::print, null);
+        System.out.println("\tPostOrderIterator.iterateDefCPS");
+
+        PostOrderIterator.iterate(tree, System.out::print, null);
+        System.out.println("\tPostOrderIterator.iterate");
+
+        PostOrderIterator<String> postOrderIterator = new PostOrderIterator<>(tree);
+        while (postOrderIterator.hasNext()) {
+            System.out.print(postOrderIterator.next());
+        }
+        System.out.println("\tPostOrderIterator");
+    }
+
+}
+
+class Tree<T> {
+    Tree<T> left;
+    T content;
+    Tree<T> right;
+
+    Tree(Tree<T> left, T content, Tree<T> right) {
+        this.left = left;
+        this.content = content;
+        this.right = right;
+    }
+
+    @Override
+    public String toString() {
+        return content.toString();
+    }
+}
+
+class InOrderIterator<T> implements Iterator<T> {
+
+    private static class Cont<T> {
+        Tree<T> tree;
+        Cont<T> next;
+
+        Cont(Tree<T> tree, Cont<T> next) {
+            this.tree = tree;
+            this.next = next;
+        }
+    }
+
+    static <T> void iterateRecursive(Tree<T> tree, Consumer<T> action) {
+        if (tree != null) {
+            iterateRecursive(tree.left, action);
+            action.accept(tree.content);
+            iterateRecursive(tree.right, action);
+        }
+    }
+
+    static <T> void iterateCPS(Tree<T> tree, Consumer<T> action, Runnable cont) {
+        if (tree != null) {
+            iterateCPS(tree.left, action, () -> {
+                action.accept(tree.content);
+                iterateCPS(tree.right, action, cont);
+            });
+        } else {
+            cont.run();
+        }
+    }
+
+    static <T> void iterateDefCPS(Tree<T> tree, Consumer<T> action, Cont<T> cont) {
+        if (tree != null) {
+            iterateDefCPS(tree.left, action, new Cont<>(tree, cont));
+        } else {
+            if (cont != null) {
+                action.accept(cont.tree.content);
+                iterateDefCPS(cont.tree.right, action, cont.next);
+            } else {
+                return;
+            }
+        }
+    }
+
+    static <T> void iterate(Tree<T> tree, Consumer<T> action, Cont<T> cont) {
+        while (true) {
+            if (tree != null) {
+                cont = new Cont<>(tree, cont);
+                tree = tree.left;
+            } else {
+                if (cont != null) {
+                    action.accept(cont.tree.content);
+                    tree = cont.tree.right;
+                    cont = cont.next;
+                } else {
+                    return;
+                }
+            }
+        }
+    }
+
+    private Tree<T> tree;
+    private Cont<T> cont;
+
+    InOrderIterator(Tree<T> tree) {
+        this.tree = tree;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return tree != null || cont != null;
+    }
+
+    @Override
+    public T next() {
+        while (hasNext()) {
+            if (tree != null) {
+                cont = new Cont<>(tree, cont);
+                tree = tree.left;
+            } else {
+                if (cont != null) {
+                    T content = cont.tree.content;
+                    tree = cont.tree.right;
+                    cont = cont.next;
+                    return content;
+                }
+            }
+        }
+        throw new NoSuchElementException();
+    }
+}
+
+class PreOrderIterator<T> implements Iterator<T> {
+
+    private static class Cont<T> {
+        Tree<T> tree;
+        Cont<T> next;
+
+        Cont(Tree<T> tree, Cont<T> next) {
+            this.tree = tree;
+            this.next = next;
+        }
+    }
+
+    static <T> void iterateRecursive(Tree<T> tree, Consumer<T> action) {
+        if (tree != null) {
+            action.accept(tree.content);
+            iterateRecursive(tree.left, action);
+            iterateRecursive(tree.right, action);
+        }
+    }
+
+    static <T> void iterateCPS(Tree<T> tree, Consumer<T> action, Runnable cont) {
+        if (tree != null) {
+            action.accept(tree.content);
+            iterateCPS(tree.left, action, () -> iterateCPS(tree.right, action, cont));
+        } else {
+            cont.run();
+        }
+    }
+
+    static <T> void iterateDefCPS(Tree<T> tree, Consumer<T> action, Cont<T> cont) {
+        if (tree != null) {
+            action.accept(tree.content);
+            iterateDefCPS(tree.left, action, tree.right != null ? new Cont<>(tree.right, cont) : cont);
+        } else {
+            if (cont != null) {
+                iterateDefCPS(cont.tree, action, cont.next);
+            } else {
+                return;
+            }
+        }
+    }
+
+    static <T> void iterate(Tree<T> tree, Consumer<T> action, Cont<T> cont) {
+        while (true) {
+            if (tree != null) {
+                action.accept(tree.content);
+                if (tree.right != null) {
+                    cont = new Cont<>(tree.right, cont);
+                }
+                tree = tree.left;
+            } else {
+                if (cont != null) {
+                    tree = cont.tree;
+                    cont = cont.next;
+                } else {
+                    return;
+                }
+            }
+        }
+    }
+
+    private Tree<T> tree;
+    private Cont<T> cont;
+
+    PreOrderIterator(Tree<T> tree) {
+        this.tree = tree;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return tree != null || cont != null;
+    }
+
+    @Override
+    public T next() {
+        while (hasNext()) {
+            if (tree != null) {
+                T content = tree.content;
+                if (tree.right != null) {
+                    cont = new Cont<>(tree.right, cont);
+                }
+                tree = tree.left;
+                return content;
+            } else {
+                if (cont != null) {
+                    tree = cont.tree;
+                    cont = cont.next;
+                }
+            }
+        }
+        throw new NoSuchElementException();
+    }
+
+}
+
+class PostOrderIterator<T> implements Iterator<T> {
+
+    static class Cont<T> {
+        Tree<T> tree;
+        boolean isRight;
+        Cont<T> next;
+
+        Cont(Tree<T> tree, boolean isRight, Cont<T> next) {
+            this.tree = tree;
+            this.next = next;
+            this.isRight = isRight;
+        }
+    }
+
+    static <T> void iterateRecursive(Tree<T> tree, Consumer<T> action) {
+        if (tree != null) {
+            iterateRecursive(tree.left, action);
+            iterateRecursive(tree.right, action);
+            action.accept(tree.content);
+        }
+    }
+
+    static <T> void iterateCPS(Tree<T> tree, Consumer<T> action, Runnable cont) {
+        if (tree != null) {
+            iterateCPS(tree.left, action, () -> iterateCPS(tree.right, action, () -> {
+                action.accept(tree.content);
+                cont.run();
+            }));
+        } else {
+            cont.run();
+        }
+    }
+
+
+    static <T> void iterateDefCPS(Tree<T> tree, Consumer<T> action, Cont<T> cont) {
+        if (cont == null && tree == null) {
+            return;
+        }
+
+        if (tree != null) {
+            cont = new Cont<>(tree, false, cont);
+            iterateDefCPS(tree.left, action, tree.right != null ? new Cont<>(tree.right, true, cont) : cont);
+        } else {
+            if (!cont.isRight) {
+                action.accept(cont.tree.content);
+            }
+            iterateDefCPS(cont.isRight ? cont.tree : null, action, cont.next);
+        }
+    }
+
+    static <T> void iterate(Tree<T> tree, Consumer<T> action, Cont<T> cont) {
+        while (tree != null || cont != null) {
+            if (tree != null) {
+                cont = new Cont<>(tree, false, cont);
+                cont = tree.right != null ? new Cont<>(tree.right, true, cont) : cont;
+                tree = tree.left;
+            } else {
+                if (!cont.isRight) {
+                    action.accept(cont.tree.content);
+                    tree = null;
+                } else {
+                    tree = cont.tree;
+                }
+                cont = cont.next;
+            }
+        }
+    }
+
+    private Tree<T> tree;
+    private Cont<T> cont;
+
+    PostOrderIterator(Tree<T> tree) {
+        this.tree = tree;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return tree != null || cont != null;
+    }
+
+    @Override
+    public T next() {
+        while (hasNext()) {
+            if (tree != null) {
+                cont = new Cont<>(tree, false, cont);
+                cont = tree.right != null ? new Cont<>(tree.right, true, cont) : cont;
+                tree = tree.left;
+            } else {
+                T content = null;
+                if (!cont.isRight) {
+                    content = cont.tree.content;
+                    tree = null;
+                } else {
+                    tree = cont.tree;
+                }
+                cont = cont.next;
+                if (content != null) {
+                    return content;
+                }
+            }
+        }
+        throw new NoSuchElementException();
+    }
+
+}
\ No newline at end of file