Java实现的二叉树常用操作【前序建树，前中后递归非递归遍历及层序遍历】

import java.util.ArrayDeque;import java.util.Queue;import java.util.Stack;//二叉树的建树，前中后 递归非递归遍历 层序遍历//Node节点class Node {    int element;    Node left;    Node right;    public Node() {    }    public Node(int element) {        this.element = element;    }}// BinaryTreepublic class Tree {    // creat tree from array    public static Node creatTree(int[] data, int i) {        if (i >= data.length || data[i] == -1)            return null;        Node temp = new Node(data[i]);        temp.left = creatTree(data, i * 2 + 1);        temp.right = creatTree(data, i * 2 + 2);        return temp;    }    // pre前序遍历递归    public static void pre(Node temp) {        if (temp == null)            return;        System.out.print(temp.element + " ");        pre(temp.left);        pre(temp.right);    }    // mid中序遍历递归    public static void mid(Node temp) {        if (temp == null)            return;        mid(temp.left);        System.out.print(temp.element + " ");        mid(temp.right);    }    // last后序遍历递归    public static void last(Node temp) {        if (temp == null)            return;        last(temp.left);        last(temp.right);        System.out.print(temp.element + " ");    }    // pre1前序遍历非递归    public static void pre1(Node temp) {        Stack<Node> stack = new Stack<>();        while (temp != null || !stack.isEmpty()) {            while (temp != null) {                stack.push(temp);                System.out.print(temp.element + " ");                temp = temp.left;            }            if (!stack.isEmpty()) {                temp = stack.pop().right;            }        }    }    // mid1中序遍历非递归    public static void mid1(Node temp) {        Stack<Node> stack = new Stack<>();        while (temp != null || !stack.isEmpty()) {            while (temp != null) {                stack.push(temp);                temp = temp.left;            }            if (!stack.isEmpty()) {                temp = stack.pop();                System.out.print(temp.element + " ");                temp = temp.right;            }        }    }    // last1后序遍历非递归    public static void last1(Node temp) {        Stack<Node> stack = new Stack<>();        Stack<Node> stack2 = new Stack<>();        while (temp != null || !stack.isEmpty()) {            while (temp != null) {                stack.push(temp);                stack2.push(temp);                temp = temp.right;            }            if (!stack.isEmpty()) {                temp = stack.pop().left;            }        }        while (!stack2.isEmpty())            System.out.print(stack2.pop().element + " ");    }    // ceng层序遍历    public static void ceng(Node temp) {        if (temp == null)            return;        Queue<Node> queue = new ArrayDeque<>();        queue.offer(temp);        while (!queue.isEmpty()) {            temp = queue.poll();            System.out.print(temp.element + " ");            if (temp.left != null)                queue.offer(temp.left);            if (temp.right != null)                queue.offer(temp.right);        }    }    // Demo    public static void main(String[] args) {        int[] array = { 1, 2, 3, 4, 5, 6, 7, -1, -1, 10, -1, -1, 13 };        Node tree = creatTree(array, 0);        System.out.println("VeVb武林网测试结果：");        pre(tree);        System.out.println();        pre1(tree);        System.out.println();        mid(tree);        System.out.println();        mid1(tree);        System.out.println();        last(tree);        System.out.println();        last1(tree);        System.out.println();        ceng(tree);    }}