如何直观形象地树状打印一棵二叉树？

网上绝大部分的二叉树打印效果都十分潦草，也不够直观形象，最近本身用JS写了个图形化小工具BinaryTreeGraph，也用Java写了个打印器BinaryTreePrinter，还有个Objective-C版本BinaryTreePrinterOC
具体代码实现请看github

BinaryTreeGraph（JS版）

• 在线演示：BinaryTreeGraph

BinaryTreePrinter（Java版）

简介

• 树状打印一棵二叉树
• 好比输入一棵二叉搜索树
  • [381, 12, 410, 9, 40, 394, 540, 35, 190, 476, 760, 146, 445, 600, 800]
• 就会输出

• 或者输出

核心API

public final class BinaryTrees {
    // 打印一棵二叉树
    public static void print(BinaryTreeInfo tree);
    public static void print(BinaryTreeInfo tree, PrintStyle style);

    // 打印一棵二叉树（打印完自动换行）
    public static void println(BinaryTreeInfo tree);
    public static void println(BinaryTreeInfo tree, PrintStyle style);

    // 得到一棵二叉树的打印字符串
    public static String printString(BinaryTreeInfo tree);
    public static String printString(BinaryTreeInfo tree, PrintStyle style);

    // 可选的打印样式
    public enum PrintStyle {
        LEVEL_ORDER, 
        INORDER
    }
}

示例

实现BinaryTreeInfo

• 根节点是谁？
• 如何查找左节点？
• 如何查找右节点？
• 如何打印单个节点？

/**
* BinarySearchTree是你本身编写的二叉树类
*/
public class BinarySearchTree<E> implements BinaryTreeInfo {
    /**这里省略了大量代码，只贴出了脉络代码**/
    
    private Node<E> root;
    private static class Node<E> {
        E element;
        Node<E> left;
        Node<E> right;
    }
    
    /********** BinaryTreeInfo **********/
    @Override
    public Object root() {
        // 根节点是谁？
        return root;
    }

    @Override
    public Object left(Object node) {
        // 如何查找左节点？
        return ((Node<E>)node).left;
    }

    @Override
    public Object right(Object node) {
        // 如何查找右节点？
        return ((Node<E>)node).right;
    }

    @Override
    public Object string(Object node) {
        // 如何打印单个节点？
        return ((Node<E>)node).element;
    }
    /********** BinaryTreeInfo **********/
}

打印

// 随机生成的一棵二叉搜索树（random generation）
BinarySearchTree<Integer> bst = ...;

// PrintStyle.LEVEL_ORDER（层序打印）
BinaryTrees.println(bst); 

// PrintStyle.INORDER（中序打印）
BinaryTrees.println(bst, PrintStyle.INORDER);

生成字符串写入文件

Files.writeToFile("F:/test/bst.txt", BinaryTrees.printString(bst));

不须要定义二叉树类

BinaryTrees.println(new BinaryTreeInfo() {
    @Override
    public Object root() {
        return 8;
    }

    @Override
    public Object left(Object node) {
        if (node.equals(8)) return 3;
        if (node.equals(3)) return 1;
        if (node.equals(6)) return 4;
        if (node.equals(14)) return 13;
        return null;
    }

    @Override
    public Object right(Object node) {
        if (node.equals(8)) return 10;
        if (node.equals(10)) return 14;
        if (node.equals(3)) return 6;
        if (node.equals(6)) return 7;
        return null;
    }
    
    @Override
    public Object string(Object node) {
        return node;
    }
});

BinaryTrees.println(new BinaryTreeInfo() {
    @Override
    public Object root() {
        return "Life";
    }
    
    @Override
    public Object left(Object node) {
        if (node.equals("Life")) return "Animal";
        if (node.equals("Person")) return "Man";
        if (node.equals("Animal")) return "Cat";
        if (node.equals("Dog")) return "Teddy";
        return null;
    }
    
    @Override
    public Object right(Object node) {
        if (node.equals("Life")) return "Person";
        if (node.equals("Person")) return "Woman";
        if (node.equals("Animal")) return "Dog";
        if (node.equals("Dog")) return "SingleDog";
        return null;
    }
    
    @Override
    public Object string(Object node) {
        return node;
    }
});

二叉堆

public class BinaryHeap<E> implements BinaryTreeInfo {
    private int size;
    private E[] elements;

    @Override
    public Object root() {
        return 0;
    }

    @Override
    public Object left(Object node) {
        int index = ((int)node << 1) + 1;
        return index >= size ? null : index;
    }

    @Override
    public Object right(Object node) {
        int index = ((int)node << 1) + 2;
        return index >= size ? null : index;
    }

    @Override
    public Object string(Object node) {
        return elements[(int)node];
    }
}

BinaryHeap<Integer> heap = new BinaryHeap<>();
for (int i = 0; i < 10; i++) {
    heap.add((int)(Math.random() * 100));
}
BinaryTrees.println(heap);

BinaryTreePrinterOC

• 实现MJBinaryTreeInfo协议

@interface MJBSTNode : NSObject {
@public
    id _element;
    MJBSTNode *_left;
    MJBSTNode *_right;
}
@end

@interface MJBinarySearchTree : NSObject <MJBinaryTreeInfo>
@end

@interface MJBinarySearchTree() {
    MJBSTNode *_root;
}
@end

@implementation MJBinarySearchTree
#pragma mark - MJBinaryTreeInfo
- (id)left:(MJBSTNode *)node {
    return node->_left;
}

- (id)right:(MJBSTNode *)node {
    return node->_right;
}

- (id)string:(MJBSTNode *)node {
    return node->_element;
}

- (id)root {
    return _root;
}
@end

• 打印

[MJBinaryTrees println:bst];

[MJBinaryTrees println:bst style:MJPrintStyleLevelOrder];

[MJBinaryTrees println:bst style:MJPrintStyleInorder];

NSString *str = [MJBinaryTrees printString:bst];
NSString *file = @"/Users/mj/Desktop/1.txt";
[str writeToFile:file atomically:YES encoding:NSUTF8StringEncoding error:nil];