二叉树的实现

tips:

以LinkedList实现栈时要注意是removeLast();

 

树节点定义：

 

class TreeNode { public TreeNode left; public TreeNode right; public int value; public TreeNode(TreeNode left, TreeNode right, int value) { this.left = left; this.right = right; this.value = value; } } 

 

二叉树 及其操作

public class BinaryTree { public static int getTreeHeight(TreeNode root) { if (root == null) return 0; if (root.left == null && root.right == null) return 1; return 1 + Math .max(getTreeHeight(root.left), getTreeHeight(root.right)); } public static void recursePreOrder(TreeNode root) { if (root == null) return; visit(root); if (root.left != null) recursePreOrder(root.left); if (root.right != null) recursePreOrder(root.right); } public static void stackPreOrder(TreeNode root) { Stack stack = new Stack(); if (root == null) return; stack.push(root); visit(root); TreeNode temp = root.left; while (temp != null) { stack.push(temp); visit(temp); temp = temp.left; } temp = (TreeNode) stack.pop(); while (temp != null) { temp = temp.right; while (temp != null) { stack.push(temp); visit(temp); temp = temp.left; } if (stack.empty()) break; temp = (TreeNode) stack.pop(); } } public static void recurseInOrder(TreeNode root) { if (root == null) return; if (root.left != null) recurseInOrder(root.left); visit(root); if (root.right != null) recurseInOrder(root.right); } public static void stackInOrder(TreeNode root) { Stack stack = new Stack(); if (root == null) return; else stack.push(root); TreeNode temp = root.left; while (temp != null) { stack.push(temp); temp = temp.left; } temp = (TreeNode) stack.pop(); while (temp != null) { visit(temp); temp = temp.right; while (temp != null) { stack.push(temp); temp = temp.left; } if (stack.empty()) break; temp = (TreeNode) stack.pop(); } } public static void widthTraverse(TreeNode root) { Queue queue = new Queue(); queue.push(root); traverseLevel(queue); } public static void traverseLevel(Queue queue){ for(int i=0; i<queue.size(); i++){ TreeNode node = (TreeNode)queue.pop(); visit(node); if(node.left != null) queue.push(node.left); if(node.right != null) queue.push(node.right); } if(queue.size() > 0) traverseLevel(queue); } private static void visit(TreeNode node) { System.out.println(node.value); } public static void main(String[] args) { TreeNode node1 = new TreeNode(null, null, 1); TreeNode node2 = new TreeNode(null, node1, 2); TreeNode node3 = new TreeNode(null, null, 3); TreeNode node4 = new TreeNode(node2, node3, 4); TreeNode node5 = new TreeNode(null, null, 5); TreeNode root = new TreeNode(node4, node5, 0); System.out.println("Tree Height is " + getTreeHeight(root)); System.out.println("Recurse In Order Traverse"); recurseInOrder(root); System.out.println("Stack In Order Traverse"); stackInOrder(root); System.out.println("Recurse Pre Order Traverse"); recursePreOrder(root); System.out.println("Stack Pre Order Traverse"); stackPreOrder(root); System.out.println("Width Traverse"); widthTraverse(root); } } 

 

用LinkedList写的Stack

 

import java.util.EmptyStackException; import java.util.LinkedList; public class Stack { private LinkedList list; public Stack() { this.list = new LinkedList(); } public boolean empty() { return list.isEmpty(); } public Object peek() { if (empty()) throw new EmptyStackException(); return list.getLast(); } public Object pop() { if (empty()) throw new EmptyStackException(); return list.removeLast(); } public void push(Object o) { list.add(o); } public static void main(String[] args) { Stack stack = new Stack(); stack.push(new Integer(1)); stack.push(new Integer(11)); stack.push(new Integer(1111)); stack.push(new Integer(22)); stack.push(new Integer(222)); stack.push(new Integer(31)); stack.push(new Integer(221)); while (!stack.empty()) { System.out.println(stack.pop()); } } } 

 

 

用LinkedList实现的Queue：import java.util.EmptyStackException; import java.util.LinkedList; public class Queue { private LinkedList list; public Queue() { this.list = new LinkedList(); } public boolean empty() { return list.isEmpty(); } public Object peek() { if (empty()) throw new EmptyStackException(); return list.getFirst(); } public Object pop() { if (empty()) throw new EmptyStackException(); return list.removeFirst(); } public void push(Object o) { list.add(o); } public int size(){ return list.size(); } public static void main(String[] args) { Queue queue = new Queue(); queue.push(new Integer(1)); queue.push(new Integer(11)); queue.push(new Integer(1111)); queue.push(new Integer(22)); queue.push(new Integer(222)); queue.push(new Integer(31)); queue.push(new Integer(221)); while (!queue.empty()) { System.out.println(queue.pop()); } } }