用java实现二叉树相关操作（前序建树，前中后递归非递归遍历，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;
	}
}
// BinaryTree

public 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 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 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 stack = new Stack<>();
		Stack 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 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);
		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);

	}

}