hello-algo/codes/java/include/PrintUtil.java

package include;

import java.util.*;

class Trunk {
    Trunk prev;
    String str;

    Trunk(Trunk prev, String str) {
        this.prev = prev;
        this.str = str;
    }
};

public class PrintUtil {
    /**
     * Print a linked list
     * @param head
     */
    public static void printLinkedList(ListNode head) {
        List<String> list = new ArrayList<>();
        while (head != null) {
            list.add(String.valueOf(head.val));
            head = head.next;
        }
        System.out.println(String.join(" -> ", list));
    }

    /**
     * The interface of the tree printer
     * This tree printer is borrowed from TECHIE DELIGHT
     * https://www.techiedelight.com/c-program-print-binary-tree/
     * @param root
     */
    public static void printTree(TreeNode root) {
        printTree(root, null, false);
    }

    /**
     * Print a binary tree
     * @param root
     * @param prev
     * @param isLeft
     */
    public static void printTree(TreeNode root, Trunk prev, boolean isLeft) {
        if (root == null) {
            return;
        }

        String prev_str = "    ";
        Trunk trunk = new Trunk(prev, prev_str);

        printTree(root.right, trunk, true);

        if (prev == null) {
            trunk.str = "———";
        } else if (isLeft) {
            trunk.str = "/———";
            prev_str = "   |";
        } else {
            trunk.str = "\\———";
            prev.str = prev_str;
        }

        showTrunks(trunk);
        System.out.println(" " + root.val);

        if (prev != null) {
            prev.str = prev_str;
        }
        trunk.str = "   |";

        printTree(root.left, trunk, false);
    }

    /**
     * Helper function to print branches of the binary tree
     * @param p
     */
    public static void showTrunks(Trunk p) {
        if (p == null) {
            return;
        }

        showTrunks(p.prev);
        System.out.print(p.str);
    }
}