Implementation of Tree Traversal in java #149
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| //submitted by xam4lor | ||
| public class MainClass { | ||
| public static void main(String[] args) { | ||
| System.out.println("Creating Tree"); | ||
| Tree tree = new Tree(3, 3); | ||
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| System.out.println("Using recursive DFS :"); | ||
| tree.dfsRecursive(); | ||
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| System.out.println("Using stack-based DFS :"); | ||
| tree.dfsStack(); | ||
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| System.out.println("Using queue-based BFS :"); | ||
| tree.bfsQueue(); | ||
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| System.out.println("Using post-order recursive DFS :"); | ||
| tree.dfsRecursivePostOrder(); | ||
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| // Uncommenting the following 2 lines will result in an exception thrown because at least one Node of the Tree has more than 2 children and therefor a DFSRecursiveInorderBinary doesn't work. | ||
| System.out.println("Using in-order binary recursive DFS : (fail)"); | ||
| tree.dfsRecursiveInOrderBinary(); | ||
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| tree = new Tree(3, 2); | ||
| System.out.println("Using in-order binary recursive DFS : (suceed)"); | ||
| tree.dfsRecursiveInOrderBinary(); | ||
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| System.out.println(""); | ||
| } | ||
| } |
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| // submitted by xam4lor | ||
| import java.util.ArrayList; | ||
| import java.util.PriorityQueue; | ||
| import java.util.Queue; | ||
| import java.util.Stack; | ||
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| public class Tree { | ||
| public Node root; | ||
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| public Tree(int rowCount, int childrenCount) { | ||
| // this.root is the root node of the Tree | ||
| this.root = new Node(1); | ||
| this.createAllChildren(this.root, rowCount, childrenCount); | ||
| } | ||
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| public void dfsRecursive() { | ||
| this.dfsRecursive(this.root); | ||
| } | ||
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| private void dfsRecursive(Node node) { | ||
| System.out.println(node.id); | ||
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| for (Node n : node.children) { | ||
| dfsRecursive(n); | ||
| } | ||
| } | ||
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| public void dfsRecursivePostOrder() { | ||
| this.dfsRecursivePostOrder(this.root); | ||
| } | ||
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| private void dfsRecursivePostOrder(Node node) { | ||
| for (Node n : node.children) { | ||
| dfsRecursivePostOrder(n); | ||
| } | ||
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| // Here we are doing something ... | ||
| System.out.println(node.id); | ||
| } | ||
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| public void dfsRecursiveInOrderBinary() { | ||
| dfsRecursiveInOrderBinary(this.root); | ||
| } | ||
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| // This assumes only 2 children | ||
| private void dfsRecursiveInOrderBinary(Node node) { | ||
| if(node.children.size() > 2) { | ||
| System.err.println("Not a binary tree at dfsRecursiveInOrderBinary()!"); | ||
| return; | ||
| } | ||
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| if(node.children.size() > 1) { | ||
| dfsRecursiveInOrderBinary(node.children.get(0)); | ||
| System.out.println(node.id); | ||
| dfsRecursiveInOrderBinary(node.children.get(1)); | ||
| } | ||
|
There was a problem hiding this comment. The standard Java coding style would place the else on the same line as the closing brace: |
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| else { | ||
| System.out.println(node.id); | ||
| } | ||
| } | ||
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| public void dfsStack() { | ||
| Stack<Node> stack = new Stack<Node>(); | ||
| stack.push(this.root); | ||
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| Node tmp; | ||
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| while(stack.size() != 0) { | ||
| System.out.println(stack.peek().id); | ||
| tmp = stack.pop(); | ||
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| for (Node c : tmp.children) { | ||
| stack.push(c); | ||
| } | ||
| } | ||
| } | ||
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| public void bfsQueue() { | ||
| Queue<Node> queue = new PriorityQueue<Node>(); | ||
| queue.add(this.root); | ||
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| Node temp; | ||
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There was a problem hiding this comment. You can move this inside the loop There was a problem hiding this comment. What do you mean by 'inside a loop' ? There was a problem hiding this comment. You only use while(stack.size() != 0) {
System.out.println(stack.peek().id);
Node tmp = stack.pop();
for (Node c : tmp.children) {
stack.push(c);
}
} |
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| while(queue.size() != 0) { | ||
| System.out.println(queue.peek().id); | ||
| temp = queue.poll(); // return null if the queue is empty | ||
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| if(temp != null) { | ||
| for (Node c : temp.children) { | ||
| queue.add(c); | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| private void createAllChildren(Node node, int rowCount, int childrenCount) { | ||
| if(rowCount <= 1) | ||
| return; | ||
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There was a problem hiding this comment. This indentation is not quite right |
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| for (int i = 0; i < childrenCount; i++) { | ||
| node.children.add(new Node(node.id * 10 + i + 1)); | ||
| createAllChildren(node.children.get(i), rowCount - 1, childrenCount); | ||
| } | ||
| } | ||
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| private class Node implements Comparable<Node> { | ||
| public ArrayList<Node> children; | ||
| public int id; | ||
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| public Node(int id) { | ||
| this.children = new ArrayList<Node>(); | ||
| this.id = id; | ||
| } | ||
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| @Override | ||
| public int compareTo(Node other) { | ||
| // Need to implement Comparable<Node> and override this | ||
| // method because of the method BFSQueue() which uses Queues | ||
| // and must know how to check if two nodes are the same or not | ||
| return Integer.compare(this.id, other.id); | ||
| } | ||
| } | ||
| } | ||
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I think the de-facto standard is to have spaces around brackets in Java, so
Similarly for while, for, etc. loops
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You are right ! That's a bad practice that I have :/