二叉樹前序 中序 后序 遍歷

import java.util.Arrays; import java.util.LinkedList;public class BinaryTreeTraversal {/*** 構建二叉樹* @param inputList 輸入序列*/public static TreeNode createBinaryTree(LinkedList<Integer> inputList){TreeNode node = null;if(inputList==null || inputList.isEmpty()){return null;}Integer data = inputList.removeFirst();//這里的判空很關鍵。如果元素是空，說明該節點不存在，跳出這一層遞歸；如果元素非空，繼續遞歸構建該節點的左右孩子。if(data != null){node = new TreeNode(data);node.leftChild = createBinaryTree(inputList);node.rightChild = createBinaryTree(inputList);}return node;}/*** 二叉樹前序遍歷* @param node 二叉樹節點*/public static void preOrderTraversal(TreeNode node){if(node == null){return;}System.out.println(node.data);preOrderTraversal(node.leftChild);preOrderTraversal(node.rightChild);}/*** 二叉樹中序遍歷* @param node 二叉樹節點*/public static void inOrderTraversal(TreeNode node){if(node == null){return;}inOrderTraversal(node.leftChild);System.out.println(node.data);inOrderTraversal(node.rightChild);}/*** 二叉樹后序遍歷* @param node 二叉樹節點*/public static void postOrderTraversal(TreeNode node){if(node == null){return;}postOrderTraversal(node.leftChild);postOrderTraversal(node.rightChild);System.out.println(node.data);}/*** 二叉樹節點*/private static class TreeNode {int data;TreeNode leftChild;TreeNode rightChild;TreeNode(int data) {this.data = data;}}public static void main(String[] args) {LinkedList<Integer> inputList = new LinkedList<Integer>(Arrays.asList(new Integer[]{3,2,9,null,null,10,null,null,8,null,4,}));TreeNode treeNode = createBinaryTree(inputList);System.out.println("前序遍歷：");preOrderTraversal(treeNode);System.out.println("中序遍歷：");inOrderTraversal(treeNode);System.out.println("后序遍歷：");postOrderTraversal(treeNode);}}

二叉樹層序遍歷

import java.util.Arrays; import java.util.LinkedList; import java.util.Queue;public class BinaryTreeTraversalLevel {/*** 構建二叉樹* @param inputList 輸入序列*/public static TreeNode createBinaryTree(LinkedList<Integer> inputList){TreeNode node = null;if(inputList==null || inputList.isEmpty()){return null;}Integer data = inputList.removeFirst();//這里的判空很關鍵。如果元素是空，說明該節點不存在，跳出這一層遞歸；如果元素非空，繼續遞歸構建該節點的左右孩子。if(data != null){node = new TreeNode(data);node.leftChild = createBinaryTree(inputList);node.rightChild = createBinaryTree(inputList);}return node;}/*** 二叉樹層序遍歷* @param root 二叉樹根節點*/public static void levelOrderTraversal(TreeNode root){Queue<TreeNode> queue = new LinkedList<TreeNode>();queue.offer(root);while(!queue.isEmpty()){TreeNode node = queue.poll();System.out.println(node.data);if(node.leftChild != null){queue.offer(node.leftChild);}if(node.rightChild != null){queue.offer(node.rightChild);}}}/*** 二叉樹節點*/private static class TreeNode {int data;TreeNode leftChild;TreeNode rightChild;TreeNode(int data) {this.data = data;}}public static void main(String[] args) {LinkedList<Integer> inputList = new LinkedList<Integer>(Arrays.asList(new Integer[]{3,2,9,null,null,10,null,null,8,null,4,}));TreeNode treeNode = createBinaryTree(inputList);System.out.println("層序遍歷：");levelOrderTraversal(treeNode);}}

二叉樹非遞歸前序遍歷

import java.util.Arrays; import java.util.LinkedList; import java.util.Stack;public class BinaryTreeTraversalStack {/*** 構建二叉樹* @param inputList 輸入序列*/public static TreeNode createBinaryTree(LinkedList<Integer> inputList){TreeNode node = null;if(inputList==null || inputList.isEmpty()){return null;}Integer data = inputList.removeFirst();//這里的判空很關鍵。如果元素是空，說明該節點不存在，跳出這一層遞歸；如果元素非空，繼續遞歸構建該節點的左右孩子。if(data != null){node = new TreeNode(data);node.leftChild = createBinaryTree(inputList);node.rightChild = createBinaryTree(inputList);}return node;}/*** 二叉樹非遞歸前序遍歷* @param root 二叉樹根節點*/public static void preOrderTraveralWithStack(TreeNode root){Stack<TreeNode> stack = new Stack<TreeNode>();TreeNode treeNode = root;while(treeNode!=null || !stack.isEmpty()){//迭代訪問節點的左孩子，并入棧while (treeNode != null){System.out.println(treeNode.data);stack.push(treeNode);treeNode = treeNode.leftChild;}//如果節點沒有左孩子，則彈出棧頂節點，訪問節點右孩子if(!stack.isEmpty()){treeNode = stack.pop();treeNode = treeNode.rightChild;}}}/*** 二叉樹節點*/private static class TreeNode {int data;TreeNode leftChild;TreeNode rightChild;TreeNode(int data) {this.data = data;}}public static void main(String[] args) {LinkedList<Integer> inputList = new LinkedList<Integer>(Arrays.asList(new Integer[]{3,2,9,null,null,10,null,null,8,null,4,}));TreeNode treeNode = createBinaryTree(inputList);preOrderTraveralWithStack(treeNode);}}

總結

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