二叉树的多种遍历——Java

package research;import java.util.LinkedList;import java.util.Queue;import java.util.Stack;/** * 二叉树的多种遍历:先序遍历、中序遍历、后序遍历、层次遍历、深度优先遍历、广度优先遍历 *  * @author Sam * */public class BinaryTree {public static void main(String[] args) {Node root = Factory.create(4);System.out.print("先序遍历:");NLR(root);System.out.println();System.out.print("中序遍历:");LNR(root);System.out.println();System.out.print("后序遍历:");LRN(root);System.out.println();System.out.print("层次遍历:");Level(root);System.out.println();System.out.print("深度优先遍历:");depthFirstSearch(root);System.out.println();System.out.print("广度优先遍历:");breadthFirstSearch(root);}/** * 先序遍历：首先访问根，再先序遍历左（右）子树，最后先序遍历右（左）子树。 *  * @param n */static void NLR(Node n) {if (null == n) {return;}System.out.print(n);NLR(n.getLeft());NLR(n.getRight());}/** * 中序遍历：首先中序遍历左（右）子树，再访问根，最后中序遍历右（左）子树。 *  * @param n */static void LNR(Node n) {if (null == n) {return;}LNR(n.getLeft());System.out.print(n);LNR(n.getRight());}/** * 后序遍历：首先后序遍历左（右）子树，再后序遍历右（左）子树，最后访问根。 *  * @param n */static void LRN(Node n) {if (null == n) {return;}LRN(n.getLeft());LRN(n.getRight());System.out.print(n);}/** * 层次遍历：即按照层次访问，通常用队列来做。访问根，访问子女，再访问子女的子女（越往后的层次越低）（两个子女的级别相同）. * Queue1与Queue2交互存储二叉树的每一层 *  * @param n */static void Level(Node n) {Queue<Node> queue1 = new LinkedList<Node>();Queue<Node> queue2 = new LinkedList<Node>();queue1.add(n);while (!queue1.isEmpty() || !queue2.isEmpty()) {System.out.println();while (!queue1.isEmpty()) {Node curNode = queue1.poll();System.out.print(curNode);if (null != curNode.getLeft()) {queue2.add(curNode.getLeft());}if (null != curNode.getRight()) {queue2.add(curNode.getRight());}}System.out.println();while (!queue2.isEmpty()) {Node curNode = queue2.poll();System.out.print(curNode);if (null != curNode.getLeft()) {queue1.add(curNode.getLeft());}if (null != curNode.getRight()) {queue1.add(curNode.getRight());}}}}/** * 深度优先遍历 *  * @param root */static void depthFirstSearch(Node root) {Stack<Node> stack = new Stack<Node>();stack.push(root);Node node;while (!stack.empty()) {node = stack.pop();System.out.print(node);if (null != node.getRight()) {stack.push(node.getRight());// 先将右子树压栈}if (null != node.getLeft()) {stack.push(node.getLeft());// 再将左子树压栈}}}/** * 广度优先遍历 *  * @param root */static void breadthFirstSearch(Node root) {Queue<Node> queue = new LinkedList<Node>();queue.add(root);Node node;while (!queue.isEmpty()) {node = queue.poll();System.out.print(node);if (null != node.getLeft()) {queue.add(node.getLeft());// 先将左子树入队}if (null != node.getRight()) {queue.add(node.getRight());// 再将右子树入队}}}}class Node {private Object data;private Node left;private Node right;public Node() {}public Node(Object o) {data = o;}public Object getData() {return data;}public void setData(Object data) {this.data = data;}public Node getLeft() {return left;}public void setLeft(Node left) {this.left = left;}public Node getRight() {return right;}public void setRight(Node right) {this.right = right;}@Overridepublic String toString() {return null == data ? "" : String.format(" %s ", data.toString());}}/** * (1)空二叉树<br> * (2)只有一个根结点的二叉树<br> * (3)只有左子树<br> * (4)只有右子树<br> * (5)完全二叉树。 *  * @author Sam * */class Factory {public static Node create(int deep) {return create(1, 1, deep);}private static Node create(int data, int h, int deep) {Node parent = new Node(data);if (h < deep) {int next = h + 1;parent.setLeft(create(data * 2, next, deep));parent.setRight(create(data * 2 + 1, next, deep));}return parent;}}

运行结果：

先序遍历: 1  2  4  8  9  5  10  11  3  6  12  13  7  14  15 中序遍历: 8  4  9  2  10  5  11  1  12  6  13  3  14  7  15 后序遍历: 8  9  4  10  11  5  2  12  13  6  14  15  7  3  1 层次遍历: 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15 深度优先遍历: 1  2  4  8  9  5  10  11  3  6  12  13  7  14  15 广度优先遍历: 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15