import java.util.ArrayList;import java.util.Iterator;import java.util.LinkedList;import java.util.Stack;/** * Created by zhouguojing on 2019/8/20. */public class TreeNode { int val; TreeNode left; TreeNode right; public TreeNode(int val) { this.val = val; }//先序遍历 public static ArrayList<Integer> preOrder(TreeNode root) { ArrayList<Integer> list = new ArrayList<Integer>(); if(root == null) return null; list.add(root.val); if(root.left!=null) list.addAll(preOrder(root.left)); if(root.right!=null) list.addAll(preOrder(root.right)); return list; } //中序遍历 public static ArrayList<Integer> inOrder(TreeNode root) { ArrayList<Integer> list = new ArrayList<Integer>(); if(root == null) return null; if(root.left!=null) list.addAll(inOrder(root.left)); list.add(root.val); if(root.right!=null) list.addAll(inOrder(root.right)); return list; } //后序遍历 public static ArrayList<Integer> postOrder(TreeNode root) { ArrayList<Integer> list = new ArrayList<Integer>(); if(root == null) return null; if(root.left!=null) list.addAll(postOrder(root.left)); if(root.right!=null) list.addAll(postOrder(root.right)); list.add(root.val); return list; }//广度优先遍历 public static ArrayList<Integer> levelTraverse(TreeNode root) { if (root == null) { return null; } ArrayList<Integer> list = new ArrayList<Integer>(); LinkedList<TreeNode> queue = new LinkedList<TreeNode>(); queue.offer(root); while (!queue.isEmpty()) { TreeNode node = queue.poll(); list.add(node.val); if (node.left != null) { queue.offer(node.left); } if (node.right != null) { queue.offer(node.right); } } return list; } //深度优先遍历 public static ArrayList<Integer> DFSTraverse(TreeNode root) { if (root == null) { return null; } ArrayList<Integer> list = new ArrayList<Integer>(); Stack<TreeNode> stack= new Stack<TreeNode>(); stack.push(root); while (!stack.isEmpty()) { TreeNode node = stack.pop(); list.add(node.val); if (node.right != null) { stack.push(node.right); } if (node.left != null) { stack.push(node.left); } } return list; } public static void main(String[] args) { TreeNode one = new TreeNode(1); TreeNode two = new TreeNode(2); TreeNode three = new TreeNode(3); TreeNode four = new TreeNode(4); TreeNode five = new TreeNode(5); one.left = three; one.right = five; five.left = two; five.right = four; // ArrayList<Integer> list = TreeNode.levelTraverse(one); // ArrayList<Integer> list = TreeNode.preOrder(one); // ArrayList<Integer> list = TreeNode.inOrder(one); // ArrayList<Integer> list = TreeNode.postOrder(one); ArrayList<Integer> list = TreeNode.DFSTraverse(one); Iterator<Integer> it = list.iterator(); while(it.hasNext()) { System.out.print(it.next()); } }}
来源：https://www.cnblogs.com/moxia1234/p/11386034.html