二叉树节点

/**
 * Definition for a binary tree node.
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int val) { this.val = val; }
}

构建二叉树工具类

import java.util.Random;

public class BinaryTreeBuilder {
    private static Random random = new Random();

    private int level; // 需要生成的二叉树的层级
    private double leftProbability; // 左子树生成概率
    private double rightProbability; // 右子树生成概率

    private int value; // need to know: 构建前自动赋值

    public BinaryTreeBuilder(int level) {
        // 左右子树生成概率，默认为 100%
        this(level, 1, 1);
    }

    public BinaryTreeBuilder(int level, double leftProbability, double rightProbability) {
        this.level = level;
        this.leftProbability = leftProbability;
        this.rightProbability = rightProbability;
    }

    public TreeNode build() {
        value = 1;
        return buildTree(level);
    }

    private TreeNode buildTree(int level) {
        if (level == 0) return null;

        TreeNode root = new TreeNode(value++);
        if (random.nextDouble() <= leftProbability) {
            root.left = buildTree(level - 1);
        }
        if (random.nextDouble() <= rightProbability) {
            root.right = buildTree(level - 1);
        }
        return root;
    }
}

构建满二叉树，并打印到控制台。

public class BinaryTreeDemo {
    public static void main(String[] args) {
        TreeNode root = new BinaryTreeBuilder(3).build();
        BinaryTreePrinter.print(root);
    }
}

控制台输出如下：

maxLevel: 3
level[1] 节点宽度[ 16]===|          1       
                     ===|      ┌───┴───┐   
level[2] 节点宽度[  8]===|      2       5   
                     ===|    ┌─┴─┐   ┌─┴─┐ 
level[3] 节点宽度[  4]===|    3   4   6   7

构建任意二叉树，并打印到控制台：

public class BinaryTreeDemo {
    public static void main(String[] args) {
        TreeNode root = new BinaryTreeBuilder(4, 0.8, 0.7).build();
        BinaryTreePrinter.print(root);
    }
}

控制台输出如下：

maxLevel: 4
level[1] 节点宽度[ 32]===|                  1               
                     ===|          ┌───────┴───────┐       
level[2] 节点宽度[ 16]===|          2               5       
                     ===|          └───┐       ┌───┴───┐   
level[3] 节点宽度[  8]===|              3       6       8   
                     ===|            ┌─┘       └─┐   ┌─┴─┐ 
level[4] 节点宽度[  4]===|            4           7   9   10