Question

*我已在下面回答了我自己的问题*

此线程中还有其他很好的解决方案。

*原始问题：*

我正在尝试打印一棵我这样构建的树：

树（根（20），树（根（15），叶（10），叶（18）），树（根（25），叶（22），叶（27））

我有以下代码：

static int childlev = 0;//This is global var used to keep track of parentheses

public static void printStruct(MyTree tree, int level) {//This prints out the data structure of the tree
    assert tree != null;
    if (tree instanceof MyLeaf) {//reached the bottom leaf
        MyLeaf leaf = (MyLeaf)tree;
        System.out.print(",leaf('" + leaf.value+ "':" + leaf.frequency + ")");
        childlev=level;

    } else if (tree instanceof MyNode) {//reached a parent
        if(childlev>level){//print parentheses when right child leaf is reached and level goes back to parent
            for(int i=0;i<childlev-level;i++)//child level minus parent level that we are backing up to
                System.out.print(")");
            childlev=0;
        }
        if(level!=0){
            System.out.print(",");
        }

        MyNode node = (MyNode)tree;
        System.out.print("tree(root("+node.frequency+")");
        // traverse left
        printStruct(node.left, level+1);

        // traverse right
        printStruct(node.right, level+1);
    }
}
//at the end of my main after calling above function i have this:
    for(int i=0; i<p; i++)//This puts in the final parentheses 
        System.out.print(")");

输出：

tree(root(170),tree(root(70),tree(root(32),tree(root(16),tree(root(8),leaf('x':4),tree(root(4),leaf('l':2),leaf('u':2),leaf('h':8),leaf('n':16)),tree(root(38),tree(root(17),leaf('w':8),leaf('o':9)),tree(root(21),tree(root(10),leaf('v':5),leaf('f':5)),tree(root(11),leaf('y':5),tree(root(6),leaf('g':3),leaf('a':3)))))),tree(root(100),tree(root(47),leaf('t':22),tree(root(25),tree(root(12),tree(root(6),leaf('c':3),tree(root(3),leaf('z':1),leaf('d':2),leaf('r':6),leaf('i':13))),tree(root(53),leaf('e':26),leaf('s':27))))

但正如你所看到的，在叶子（'u'：2）之后应该有2个括号但是没有。所以，现在如果我们有一个正确的叶子后跟右叶子，我们就不打印任何右括号。我该如何解决？提前谢谢！

Answer 1

它并不像你制作它那么难。

首先，您应该删除MyNode和MyLeaf类。你不需要它们，它会使树的更新变得不必要。节点是叶子是树。您只需要MyTree，如下所示：

public class MyTree
{
    private MyTree left;
    private MyTree right;
    private String value;
    private int frequency;
    // ... constructors etc

    public void print()
    {
        System.out.print("tree(");
        if (left != null || right != null)
        {
            System.out.print("root("+frequency);
            if (left != null)
            {
                System.out.print(",");
                left.print();
            }
            if (right != null)
            {
                System.out.print(",");
                right.print();
            }
            System.out.print(")"); // ends root()
        }
        else
        {
            System.out.print("leaf('"+value+"':"+frequency+")");
        }
        System.out.print(")"); // ends tree()
    }

如果你真的必须保留额外的课程：

public abstract class MyTree
{
    // ...
    public abstract void print();
}

public class MyNode extends MyTree
{
    // ...
    public void print()
    {
        System.out.print("tree(");
        System.out.print("root("+this.frequency);
        if (left != null)
        {
            System.out.print(",");
            left.print();
        }
        if (right != null)
        {
            System.out.print(",");
            right.print();
        }
        System.out.print(")"); // ends root()
        System.out.print(")"); // ends tree()
    }
}

public class MyLeaf extends MyTree
{
    // ...

    public void print()
    {
        System.out.print("tree(");
        System.out.print("leaf('"+value+"':"+frequency+")");
        System.out.print(")"); // ends tree()
    }
}

请注意，您不需要支架计数器，并且该方法不是静态的。

E＆安培; OE

Answer 2

*我正在回答我自己的问题*

至少可以说我的解决方案有点混乱。

在这个帖子中还有其他很好的解决方案，但由于我的案例有点特殊，我必须找到自己的方法来做到这一点。基本上固定边缘情况。我会为这个项目提供一个链接到我的GitHub，一旦它启动，所以其他人可能会清楚地看到它。

以下是工作版本：

//These are global vars declared up top
static int chl = 0;//keeps track of child level
static int retp = 0;//keeps track of return parent level
static int rl = 0;//keeps track of right leaves

//Here is the function to print out tree:
public static void printStruct(MyTree tree, int level, int right) {//This prints out the data structure of the tree
    assert tree != null;
    if (tree instanceof MyLeaf) {//reached the bottom leaf
        if(right==1 && rl>1){//print parentheses when right leaf is followed by right leaf
            for(int i=0;i<chl-retp;i++)
                System.out.print(")");
            retp--;
        }
        MyLeaf leaf = (MyLeaf)tree;
        System.out.print(",leaf('" + leaf.value+ "':" + leaf.frequency + ")");
        chl=level;
    } else if (tree instanceof MyNode) {//reached a parent
        rl=0;//next node is not leaf set back to zero
        if(chl>level){//print parentheses when right child leaf is reached and level goes back to ancestor parent
            for(int i=0;i<chl-level;i++)
                System.out.print(")");
            chl=0;
        }
        if(level!=0){//if not the first root then add comma
            System.out.print(",");
        }           
        MyNode node = (MyNode)tree;
        System.out.print("tree(root("+node.frequency+")");
        // traverse left
        if(node.left instanceof MyNode){
            retp=level;
        }
        printStruct(node.left, level+1, 0);

        // traverse right
        if(node.right instanceof MyNode){
            retp=level;
        }else rl++;//next node is right leaf
        printStruct(node.right, level+1, 1);
    }
}

//at the end of my main when calling above function I have this:
printStruct(tree, 0, 0);
for(int i=0; i<chl; i++)//This puts in the final parentheses 
    System.out.print(")");

这是正确的输出：

tree(root(170),tree(root(70),tree(root(32),tree(root(16),tree(root(8),leaf('x':4),tree(root(4),leaf('l':2),leaf('u':2))),leaf('h':8)),leaf('n':16)),tree(root(38),tree(root(17),leaf('w':8),leaf('o':9)),tree(root(21),tree(root(10),leaf('v':5),leaf('f':5)),tree(root(11),leaf('y':5),tree(root(6),leaf('g':3),leaf('a':3)))))),tree(root(100),tree(root(47),leaf('t':22),tree(root(25),tree(root(12),tree(root(6),leaf('c':3),tree(root(3),leaf('z':1),leaf('d':2))),leaf('r':6)),leaf('i':13))),tree(root(53),leaf('e':26),leaf('s':27))))

Java-以括号递归地打印树

2 个答案: