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Trees.java
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/** Copyright 2011 Fabian Steeg, University of Cologne, http://github.com/spinfo */
package spinfo;
import static org.junit.Assert.assertEquals;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import org.junit.Test;
/** Trees: a versatile data structure. */
public class Trees {
/* Basic implementation strategy: nodes and links/pointers/references */
/* Simple binary tree, two pointers in each node. */
static class SimpleTree {
SimpleNode root;
static class SimpleNode {
Object value;
SimpleNode left;
SimpleNode right;
}
}
/* Simple multi-children tree, with a list of children in each node. */
static class MultiTree {
MultiNode root;
static class MultiNode {
Object value;
List<MultiNode> children; // n references per node for n children
}
}
/* Multi-children tree implemented like a linked list: less references. */
static class LinkedTree {
LinkedNode root;
static class LinkedNode {
Object value;
LinkedNode head;
LinkedNode tail; // 2 references per node for n children
}
}
@Test
public void binarySearchTree() {
BinaryTree tree = new BinaryTree();
tree.addRecursive(5);
tree.addRecursive(3);
tree.addRecursive(8);
tree.addRecursive(2);
tree.addRecursive(4);
tree.addRecursive(7);
tree.addRecursive(6);
assertEquals(Arrays.asList(5, 3, 2, 4, 8, 7, 6), tree.preorder());
}
@Test
public void dotVisualization() {
BinaryTree tree = new BinaryTree();
tree.addIterative(5);
tree.addIterative(3);
tree.addIterative(8);
tree.addIterative(2);
tree.addIterative(4);
tree.addIterative(7);
tree.addIterative(6);
assertEquals("digraph{5->3;3->2;3->4;5->8;8->7;7->6;}", tree.visualize());
}
static class BinaryTree {
BinaryNode root;
static class BinaryNode {
public BinaryNode(int value) {
this.value = value;
}
int value;
BinaryNode left;
BinaryNode right;
public String toString() {
return String.valueOf(value);
}
}
/* Corresponding to the rekursive structure, we add recursively */
public void addRecursive(int value) {
if (root == null)
root = new BinaryNode(value); // done
else
addRecursive(root, value); // go on
}
private void addRecursive(BinaryNode node, int value) {
if (value < node.value) { // new val should go left
if (node.left == null)
node.left = new BinaryNode(value); // done
else
addRecursive(node.left, value); // go on left
} else { // new val should go right
if (node.right == null)
node.right = new BinaryNode(value); // done
else
addRecursive(node.right, value); // go on right
}
}
/* But a recursive concept can also be implemented iteratively */
public void addIterative(int value) {
if (root == null)
root = new BinaryNode(value); // done
else
addIterative(root, value); // go on
}
private void addIterative(BinaryNode root, int value) {
BinaryNode current = root;
while (current != null) {
if (value < current.value) {
if (current.left == null) {
current.left = new BinaryNode(value);
return; // done
}
current = current.left; // go on
} else {
if (current.right == null) {
current.right = new BinaryNode(value);
return; // done
}
current = current.right; // go on
}
}
}
/* Two preorder traversals: collect values, visualize with Graphviz DOT */
public List<Integer> preorder() {
return preorder(root, new ArrayList<Integer>());
}
public List<Integer> preorder(BinaryNode node, List<Integer> result) {
if (node == null)
return result;
result.add(node.value); // Pre-order: 1. root
preorder(node.left, result); // 2. left
preorder(node.right, result); // 3. right
return result;
}
public String visualize() { // another Pre-order traversal
StringBuilder builder = new StringBuilder();
return String.format("digraph{%s}", visualize(root, builder));
}
private String visualize(BinaryNode node, StringBuilder builder) {
if (node != null) { // Pre-order: 1. root
if (node.left != null)
builder.append(String.format("%s->%s;", node, node.left));
visualize(node.left, builder); // 2. left
if (node.right != null)
builder.append(String.format("%s->%s;", node, node.right));
visualize(node.right, builder); // 3. right
}
return builder.toString();
}
}
}