控制台直观打印二叉树

TreeNode.java

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }

    /**
     * 将树转换成字符串并打印在控制台上，用L表示左孩子，R表示右孩子
     */
    public void print() {
        List<TreeNode> tree = locateNodes();
        int size = tree.size();
        int deepth = 0;
        // 获取树的深度
        while ((size >>= 1) > 0) {
            deepth++;
        }
        deepth++;
        Iterator<TreeNode> iterator = tree.iterator();
        int maxPosition = 1;
        // 层数，从1开始
        for (int floor = 1; floor <= deepth; floor++) {
            maxPosition = 1 << (floor - 1);
            printBlank((1 << (deepth - floor)) - 1);
            for (int position = 0; position < maxPosition; position++) {
                if (iterator.hasNext()) {
                    TreeNode node = iterator.next();
                    if (node != null) {
                        System.out.print(node);
                    } else {
                        System.out.print(" ");
                    }
                    printBlank((1 << (deepth - floor + 1)) - 1);
                }
            }
            System.out.println();
        }
    }

    /**
     * 将二叉树用空节点补充成完全二叉树，并以水平遍历形式返回
     *
     * @return
     */
    private List<TreeNode> locateNodes() {
        Queue<TreeNode> queue = new LinkedList<>();

        // 把树补充成完全二叉树，放在这个链表中
        List<TreeNode> tree = new LinkedList<>();
        queue.add(this);

        // 队列中非空节点数
        int nodeCount = 1;
        while (!queue.isEmpty() && nodeCount > 0) {
            TreeNode node = queue.remove();
            if (node != null) {
                nodeCount--;
                tree.add(node);
                TreeNode leftNode = node.left;
                TreeNode rightNode = node.right;
                if (leftNode == null) {
                    queue.add(null);
                } else {
                    queue.add(leftNode);
                    nodeCount++;
                }
                if (rightNode == null) {
                    queue.add(null);
                } else {
                    queue.add(rightNode);
                    nodeCount++;
                }
            } else {
                tree.add(null);
                queue.add(null);
                queue.add(null);
            }
        }
        return tree;
    }

    private void printBlank(int length) {
        while (length-- > 0) {
            System.out.print(" ");
        }
    }

    @Override
    public String toString() {
        return "" + val;
    }

}