二叉树 树形打印 java

下面是二叉树树形打印的Java代码实现：

public class BinaryTreePrinter {
    public static void printNode(TreeNode root) {
        int maxLevel = maxLevel(root);

        printNodeInternal(Collections.singletonList(root), 1, maxLevel);
    }

    private static void printNodeInternal(List<TreeNode> nodes, int level, int maxLevel) {
        if (nodes.isEmpty() || isAllElementsNull(nodes))
            return;

        int floor = maxLevel - level;
        int edgeLines = (int) Math.pow(2, (Math.max(floor - 1, 0)));
        int firstSpaces = (int) Math.pow(2, (floor)) - 1;
        int betweenSpaces = (int) Math.pow(2, (floor + 1)) - 1;

        printWhitespaces(firstSpaces);

        List<TreeNode> newNodes = new ArrayList<>();
        for (TreeNode node : nodes) {
            if (node != null) {
                System.out.print(node.val);
                newNodes.add(node.left);
                newNodes.add(node.right);
            } else {
                newNodes.add(null);
                newNodes.add(null);
                System.out.print(" ");
            }

            printWhitespaces(betweenSpaces);
        }
        System.out.println("");

        for (int i = 1; i <= edgeLines; i++) {
            for (int j = 0; j < nodes.size(); j++) {
                printWhitespaces(firstSpaces - i);
                if (nodes.get(j) == null) {
                    printWhitespaces(edgeLines + edgeLines + i + 1);
                    continue;
                }

                if (nodes.get(j).left != null)
                    System.out.print("/");
                else
                    printWhitespaces(1);

                printWhitespaces(i + i - 1);

                if (nodes.get(j).right != null)
                    System.out.print("\\");
                else
                    printWhitespaces(1);

                printWhitespaces(edgeLines + edgeLines - i);
            }

            System.out.println("");
        }

        printNodeInternal(newNodes, level + 1, maxLevel);
    }

    private static void printWhitespaces(int count) {
        for (int i = 0; i < count; i++)
            System.out.print(" ");
    }

    private static int maxLevel(TreeNode node) {
        if (node == null)
            return 0;

        return Math.max(maxLevel(node.left), maxLevel(node.right)) + 1;
    }

    private static boolean isAllElementsNull(List list) {
        for (Object object : list) {
            if (object != null)
                return false;
        }

        return true;
    }

    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.left = new TreeNode(4);
        root.left.right = new TreeNode(5);
        root.right.left = new TreeNode(6);
        root.right.right = new TreeNode(7);

        printNode(root);
    }
}

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

    TreeNode(int x) {
        val = x;
    }
}

通过调用`printNode`方法，可以打印出二叉树的树形结构。其中`TreeNode`类表示二叉树节点，`val`表示节点的值，`left`和`right`分别表示节点的左右子节点。