二叉树深度优先遍历（递归、非递归）、广度优先遍历、构建二叉树

public class BinaryTree {
    static class TreeNode{
        int value;
        TreeNode left;
        TreeNode right;
        public TreeNode(int value){
            this.value = value;
        }
    }
    TreeNode root;
    public BinaryTree(int []array){
        root = createBinaryTree(array,0);
    }
    //利用二叉树的数组表示法构建二叉树，并返回根节点。
    public  TreeNode createBinaryTree(int []array,int index){
        if (index < array.length){
            int value = array[index];
            TreeNode root = new TreeNode(value);
            root.left = createBinaryTree(array,index*2+1);
            root.right = createBinaryTree(array,index*2+2);
            return root;
        }
        return null;
    }
    //深度优先遍历的非递归实现，采用栈。
    public  void depthOrderTraversal(TreeNode root){
        if (root == null){
            System.out.println("空树！");
        }
        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        while (!stack.isEmpty()){
            TreeNode node = stack.pop();
            System.out.println(node.value);
            //先让右结点入栈，以致在pop时确保左结点先出栈
            if (node.right != null){
                stack.push(node.right);
            }
            if (node.left != null){
                stack.push(node.left);
            }
        }
    }
    //深度优先遍历的递归实现
    public  void depthOrderTraversalWithRecursion(TreeNode root){
        if (root != null){
            System.out.println(root.value);
        }
        depthOrderTraversal(root.left);
        depthOrderTraversal(root.right);
    }

    //广度优先遍历的非递归实现。采用队列实现。广度优先遍历无法用递归实现
    public void breadthOrderTraversal(TreeNode root){
        if (root == null){
            System.out.println("空树！");
        }
        Queue<TreeNode> queue = new ArrayDeque<>();
        queue.add(root);
        while (!queue.isEmpty()){
            TreeNode node = queue.remove();
            System.out.println(node.value);
            if (node.left != null){
                queue.add(node.left);
            }
            if (node.right != null){
                queue.add(node.right);
            }
        }
    }

    public static void main(String[] args) {
        int []array = {1,2,3,4,5,6,7};
        BinaryTree binaryTree = new BinaryTree(array);
//        binaryTree.depthOrderTraversal(binaryTree.root);
//        binaryTree.depthOrderTraversalWithRecursion(binaryTree.root);
        binaryTree.breadthOrderTraversal(binaryTree.root);

    }
}