java创建二叉树及遍历

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已知外部提供创建树所需要的数据。

方法1：按照从上到下从左到右依次把数据放在对应结点来创建树。
即数组中index处的数据在树中仍然是放在index处，而它的左右子结点分别是 2*index+1 , 2*index+2

-- BinaryTree.javapublic class BinaryTree {    Node root;     int size;  // 结点总个数    Object[] data;     // 内部类     private class Node{          private Node left;          private Node right;          private Object data;          public Node(Object data){              this.left = null;              this.right = null;              this.data = data;          }      }    public BinaryTree(Object[] data){        this.data = data;        size = data.length;        root = createTree(0);           }    // 创建下标为index处的结点及其子树,递归    public Node createTree(int index){        if (index >= size)            return null;        Node node = new Node(data[index]);        node.left = createTree(2*index+1);        node.right = createTree(2*index+2);        return node;            }    // 先序遍历    public void preShow(Node node) {         if(node!=null){            System.out.print(node.data + " ");            preShow(node.left);            preShow(node.right);        }    }    // 先序非递归    public void preShow(TreeNode root){        Stack<TreeNode> s = new Stack<>();        TreeNode p = root;        while(p!=null || !s.isEmpty()){            while(p!=null){                System.out.println(p.val);                s.push(p);                p=p.left;                           }            p=s.pop();                      p=p.right;        }    }    // 中序遍历    public void middleShow(Node node) {         if (node != null) {            middleShow(node.left);            System.out.print(node.data + " ");            middleShow(node.right);        }    }    // 中序非递归    public void midShow(TreeNode root){        Stack<TreeNode> s = new Stack<>();        TreeNode p = root;        while(p!=null || !s.isEmpty()){            while(P!=null){                s.push(p);                p=p.left;                           }            p=s.pop();            System.out.println(p.val);            p=p.right;        }    }    // 后序遍历        public void backShow(Node node) {             if (node != null) {                middleShow(node.left);                middleShow(node.right);                System.out.print(node.data + " ");                          }        }    // 层次遍历    public void levelShow(Node node){        Queue<Node> queue = new LinkedList<>();        if(node == null)            return;        queue.add(node);        while(!queue.isEmpty()){            Node n = queue.poll();            System.out.print(n.data+" ");            if(n.left!=null)                queue.offer(n.left);            if(n.right!=null)                queue.offer(n.right);        }    }       // 求树的深度    public int getDepth(Node node){        if(node==null)            return 0;        return getDepth(node.left)>getDepth(node.right)?getDepth(node.left)+1:getDepth(node.right)+1;    }       //  判断是否平衡二叉树    // 网友方法，只要有个结点不平衡，result就会变为falseprivate boolean result = true;public boolean isBalanced(TreeNode root) {    maxDepth(root);    return result;}public int maxDepth(TreeNode root) {    if (root == null)        return 0;    int l = maxDepth(root.left);    int r = maxDepth(root.right);    if (Math.abs(l - r) > 1)        result = false;    return 1 + Math.max(l, r);}       // 树中序遍历时是否是升序的？    public boolean isValidBST(TreeNode root) {        return isValidBST(root, Long.MIN_VALUE, Long.MAX_VALUE);    }    public boolean isValidBST(TreeNode root, long minVal, long maxVal) {        if (root == null) return true;        if (root.val >= maxVal || root.val <= minVal) return false;        return isValidBST(root.left, minVal, root.val) && isValidBST(root.right, root.val, maxVal);    }    public static void main(String[] args) {            Object[] my = new Object[]{'1', '2', '3', '4', '0', '5', '6', '7', '8', '0', '0', '9', 'A'};            BinaryTree tree = new BinaryTree(my);            tree.preShow(tree.root);            System.out.println();            tree.middleShow(tree.root);        }}

法2：采用先序遍历创建二叉树

--  BinaryTree2.javapublic class BinaryTree2 {    Node root;     int size;  // 结点总个数    Object[] data;     int index;  //表示取到数组中下标为index的元素了    // 内部类     private class Node{          private Node left;          private Node right;          private Object data;          public Node(Object data){              this.left = null;              this.right = null;              this.data = data;          }      }    public BinaryTree2(Object[] data){        size = data.length;        this.data = data;        index = 0;        root = createTree();    }    // 按照先序遍历创造树    public Node createTree(){        if(index>=size)            return null;        Object o = data[index++];               Node node = new Node(o);        node.left = createTree();        node.right = createTree();        return node;    }    // 先序遍历        public void preShow(Node node) {             if(node!=null){                System.out.print(node.data + " ");                preShow(node.left);                preShow(node.right);            }        }        // 中序遍历        public void middleShow(Node node) {             if (node != null) {                middleShow(node.left);                System.out.print(node.data + " ");                middleShow(node.right);            }        }        // 后序遍历            public void backShow(Node node) {                 if (node != null) {                    middleShow(node.left);                    middleShow(node.right);                    System.out.print(node.data + " ");                              }            }            public static void main(String[] args) {                Object[] my = new Object[]{'1', '2', '3', '4', '0', '5', '6', '7', '8', '0', '0', '9', 'A'};                BinaryTree2 tree = new BinaryTree2(my);                tree.preShow(tree.root);                System.out.println();                tree.middleShow(tree.root);            }}

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