java - 在java中的二叉树递归函数中存储计数器

Question

我正在为学校做一个练习，我必须在java中创建一个方法(最多O(n)时间)来存储给定值在二叉树中出现的顺序，无论是后序、中序还是前序遍历。到目前为止，我已经有了工作代码，但计数器没有正确增加。有人可以让我知道我做错了什么吗？我的代码如下:

public class Node {

int value;                // data used as key value
Node left;                // this node's left child
Node right;               // this node's right child
int preorderNumber; // node number in preorder
int inorderNumber; // node number in inorder
int postorderNumber; // node number in postorder


public Node(int item) { //instantiates node.
    value = item;
    left = right = null;
    preorderNumber = inorderNumber = postorderNumber = 0;
}

}

/* Given a binary tree, print its nodes according to the postorder traversal. */
private void printPostorder(Node node) {
    int counter = 0;

    if (node == null) { //the tree is empty. 
        return;
    }
    printPostorder(node.left); // first recur on left subtree 
    printPostorder(node.right); // then recur on right subtree
    System.out.print(node.value + " "); // now deal with the node
    counter++;
    node.postorderNumber = counter;
}

/* Given a binary tree, print its nodes in inorder*/
private void printInorder(Node node) {
    int counter = 0;

    if (node == null) {
        return;
    }
    printInorder(node.left);   // first recur on left child
    System.out.print(node.value + " "); // then print the data of node
    counter++;
    node.inorderNumber = counter;
    printInorder(node.right); // now recur on right child 
}

/* Given a binary tree, print its nodes in preorder*/
private void printPreorder(Node node) {
    int counter = 0;

    if (node == null) { //binary tree is empty. 
        return;
    }
    System.out.print(node.value + " "); // first print data of node.
    counter++;
    node.preorderNumber = counter;
    printPreorder(node.left); //  recur on left subtree 
    printPreorder(node.right); // now recur on right subtree 
}

public int find(int valueToFind) { 
    Node current = root, prior = null; 
    while (current != null) {
        int compare;
        compare = (valueToFind - current.value);
        if (compare < 0) {
            prior = current;
            current = current.left;
        } else if (compare > 0) {
            current = current.right;
        } else {
            System.out.println("The node value searched for is : " + valueToFind);
            System.out.println("The in order value is: " + current.inorderNumber);
            System.out.println("The post order value is: " + current.postorderNumber);
            System.out.println("The pre order value is: " + current.preorderNumber);
            return current.value;
        }
    }
    return prior == null ? null : prior.value;
}

}

但是，每当我尝试运行此程序时，我都会得到类似以下输出的内容:

节点数量为:2 二叉树的前序遍历为 3 4 二叉树的中序遍历为 3 4 二叉树的后序遍历为 4 3 搜索到的节点值为:4 顺序值为:1 订单后值为:1 预购金额为:1

我不确定如何将计数器的值传递给节点，以便它保存正确的值(在本例中为 2、2 和 1)。谢谢你!

Answer 1

您需要从prv值获取计数器。否则会一直重置。像下面这样做

private void printPostorder(Node node) {

    if (node == null) { //the tree is empty. 
        return;
    }

    int counter = node.postorderNumber;

    printPostorder(node.left); // first recur on left subtree 
    printPostorder(node.right); // then recur on right subtree
    System.out.print(node.value + " "); // now deal with the node
    counter++;
    node.postorderNumber = counter;
}

预购方法也应该像这样改变，否则计数器不会增加