Assume that your Binary tree is represented in the following manner:
public class BinaryTreeModel {
private Object value;
private BinaryTreeModel left;
private BinaryTreeModel right;
public BinaryTreeModel(Object value) {
this.value = value;
}
// standard getters and setters
}
Then the code for the pretty print the tree could be written like this:
For root node:
public String traversePreOrder(BinaryTreeModel root) {
if (root == null) {
return "";
}
StringBuilder sb = new StringBuilder();
sb.append(root.getValue());
String pointerRight = "└──";
String pointerLeft = (root.getRight() != null) ? "├──" : "└──";
traverseNodes(sb, "", pointerLeft, root.getLeft(), root.getRight() != null);
traverseNodes(sb, "", pointerRight, root.getRight(), false);
return sb.toString();
}
for child nodes:
public void traverseNodes(StringBuilder sb, String padding, String pointer, BinaryTreeModel node,
boolean hasRightSibling) {
if (node != null) {
sb.append("\n");
sb.append(padding);
sb.append(pointer);
sb.append(node.getValue());
StringBuilder paddingBuilder = new StringBuilder(padding);
if (hasRightSibling) {
paddingBuilder.append("│ ");
} else {
paddingBuilder.append(" ");
}
String paddingForBoth = paddingBuilder.toString();
String pointerRight = "└──";
String pointerLeft = (node.getRight() != null) ? "├──" : "└──";
traverseNodes(sb, paddingForBoth, pointerLeft, node.getLeft(), node.getRight() != null);
traverseNodes(sb, paddingForBoth, pointerRight, node.getRight(), false);
}
}
Then all you need to do is call the function for the root node like this:
System.out.println(traversePreOrder(root));
This article explains in detail the whole approach - https://www.baeldung.com/java-print-binary-tree-diagram. This idea could be extended to pretty print generic trees, tries and much more.
How to do the same for trie?
Assume the helper classes for the trie are Trie and TrieNode defined as follows:
public class TrieNode{
public HashMap<Character, TrieNode> children;
public boolean isWord;
public TrieNode() {
children = new HashMap<>();
isWord = false;
}
}
and
public class Trie{
public TrieNode root;
public Trie() {
root = new TrieNode();
}
// Insert method for trie, search method for trie, delete method for trie not shown as they are not relevant
}
Now, to implement pretty print methods, just insert the two methods in the Trie class:
public String traversePreOrder() {
if (root == null) {
return "";
}
StringBuilder sb = new StringBuilder();
sb.append("○");
Set<Character> childNodeChars = root.children.keySet();
Iterator<Character> iterator = childNodeChars.iterator();
while (iterator.hasNext()) {
Character childC = iterator.next();
if (!iterator.hasNext())
traverseNodes(sb, "", "└──", root, childC, false);
else
traverseNodes(sb, "", "├──", root, childC, true);
}
return sb.toString();
}
private void traverseNodes(StringBuilder sb, String padding, String pointer, TrieNode node, Character c, boolean hasNextSibling) {
sb.append("\n");
sb.append(padding);
sb.append(pointer);
sb.append(c);
sb.append(node.children.get(c).isWord?"(1)":"");
StringBuilder paddingBuilder = new StringBuilder(padding);
paddingBuilder.append(hasNextSibling?"│ ":" ");
String paddingForBoth = paddingBuilder.toString();
TrieNode childNode = node.children.get(c);
if(childNode == null)
return;
Set<Character> childNodeChars = childNode.children.keySet();
Iterator<Character> iterator = childNodeChars.iterator();
while (iterator.hasNext()) {
Character childC = iterator.next();
if (!iterator.hasNext())
traverseNodes(sb, paddingForBoth, "└──", childNode, childC, false);
else
traverseNodes(sb, paddingForBoth, "├──", childNode, childC, true);
}
}
