我正在尝试为实验室作业编写以下方法，但已经非常困难。我们正在使用二进制搜索树，他们已经要求使用这种方法"int sizeBelow(T high) returns the number of elements in the tree that are strictly less than high"如果有人可以帮我弄清楚如何写这个，那将非常感激！被困在这个问题太久了
package week11;
import java.util.Scanner;
import static week11.LinkedBST.Direction.*;
/**
* A binary tree implementation using links. We assume that the tree
* is not to store 'null' elements. In particular if the root node
* *is* null then the tree is empty. This can only occur if a tree
* is initially constructed with no arguments, or if we remove the
* only element from a tree.
*
* @author Michael Albert, Iain Hewson
*/
public class LinkedBST<T extends Comparable<T>> {
/** The element held at the root of this tree. */
private T root;
/** The left subtree of this tree. */
private LinkedBST<T> left;
/** The right subtree of this tree. */
private LinkedBST<T> right;
/**
* Creates a BST with the given value.
*
* @param value to store at the root of this LinkedBST.
*/
public LinkedBST(T value) {
root = value;
left = null;
right = null;
}
/**
* Creates a new empty BST.
*/
public LinkedBST() {
this(null);
}
/**
* Adds an element to this BST if it isn't already there.
*
* @param element an element to be added.
*/
public void add(T element) {
if (root == null) {
root = element;
}
int comparison = root.compareTo(element);
if (comparison > 0) {
if (left == null) {
left = new LinkedBST<T>(element);
} else {
left.add(element);
}
} else if (comparison < 0) {
if (right == null) {
right = new LinkedBST<T>(element);
} else {
right.add(element);
}
}
}
/**
* Returns the height of this tree.
*
* @return the height of this tree.
*/
public int height() {
int leftH = 0, rightH = 0;
if (root == null) {
return 0;
}
if (right != null) {
rightH = 1 + right.height();
}
if (left != null) {
leftH = 1 + left.height();
}
return Math.max(leftH, rightH);
}
/**
* Searches for the given target within this tree.
*
* @param target
* @return true if target is found, otherwise false.
*/
public boolean search(T target) {
boolean lefth = false, righth = false;
if (root == null) {
return false;
}
int comparison = root.compareTo(target);
if (comparison == 0) {
return true;
}
if (comparison > 0) {
if (left != null) {
lefth = left.search(target);
}
return lefth;
}
if (comparison < 0) {
if (right != null) {
righth = right.search(target);
}
return righth;
}
return false;
}
/**
* Returns the size of this BST.
*
* @return the size of this BST.
*/
public int size() {
int lefth = 0, righth = 0;
if (root == null) {
return 0;
}
if (right != null) {
righth = right.size();
}
if (left != null) {
lefth = left.size();
}
return 1 + lefth + righth;
}
/**
* Returns how many elements are greater than or equal to the
* parameter <code>low</code>.
*
* @param low the lower bound to use when counting elements.
* @return how many elements are greater than or equal to the
* parameter <code>low</code>.
*/
public int sizeAbove(T low) {
if (root == null) {
return 0;
}
return 0;
}
/**
* Returns how many elements are less than the parameter
* <code>high</code>.
*
* @param high the element to compare when counting elements.
* @return how many elements are less than the parameter
* <code>high</code>.
*/
public int sizeBelow(T high) {
// implement this for part 2
return 0;
}
/**
* Returns how many elements are greater than or equal to the
* parameter <code>low</code> and less than the parameter
* <code>high</code>.
*
* @param low the lower bound to use when counting elements.
* @param high the upper bound to use when counting elements.
* @return how many elements are between low (inclusive) and
* high (exclusive).
*/
public int sizeBetween(T low, T high) {
// implement this for part 2
return 0;
}
/**
* Removes the given element from this tree if it is present.
*
* @param element the element to remove.
*/
public void remove(T element) {
// implement this method from the lectures if you
// want to do the extension exercises
}
/** The direction used when creating a representation of this tree. */
enum Direction {LEFT, RIGHT, NO};
/**
* Recursively generates a representation of this tree.
*
* @param curr the current line being generated.
* @param dir the direction of the last link followed.
* @param result the representation generated so far.
* @return a representation of this tree.
*/
public StringBuilder str(String curr, Direction dir, StringBuilder result) {
if(right != null) {
right.str(curr + (dir == LEFT ? "│ " : " "), RIGHT, result);
}
if (root != null) {
result.append(curr + (dir == RIGHT ? "┌─ " :
dir == LEFT ? "└─ " : " ") + root + "\n");
}
if(left != null) {
left.str(curr + (dir == RIGHT ? "│ " : " "), LEFT, result);
}
return result;
}
@Override
public String toString() {
return str("", NO, new StringBuilder()).toString();
}
/**
* Entry point of program (used for testing).
* Valid commands are:
* <pre>
* a (add) item(s) - calls add with each item
* f (find) item - calls search with item
* p (print) - calls toString
* h (height) - calls height
* s (size) - calls size
* sa (sizeabove) low - calls sizeAbove(low)
* sb (sizebelow) high - calls sizeBelow(high)
* si (sizeinbetween) low high - calls sizeBetween(low,high)
* </pre>
* Return values of methods are printed to stdout.
*
* @param args command line arguments are not used.
*/
public static void main(String[] args) {
LinkedBST<String> tree = new LinkedBST<>();
Scanner input = new Scanner(System.in);
while (input.hasNextLine()) {
Scanner line = new Scanner(input.nextLine());
if (line.hasNext()) {
String command = line.next();
switch (command) {
case "a": case "add":
while (line.hasNext()) {
tree.add(line.next());
}
break;
case "f": case "find":
if (line.hasNext()) {
System.out.println(tree.search(line.next()));
}
break;
case "p": case "print":
System.out.print(tree);
break;
case "h": case "height":
System.out.println(tree.height());
break;
case "s": case "size":
System.out.println(tree.size());
break;
case "sa": case "sizeabove":
if (line.hasNext()) {
String low = line.next();
System.out.println(tree.sizeAbove(low));
}
break;
case "sb": case "sizebelow":
if (line.hasNext()) {
package week11;
import java.util.Scanner;
import static week11.LinkedBST.Direction.*;
/**
* A binary tree implementation using links. We assume that the tree
* is not to store 'null' elements. In particular if the root node
* *is* null then the tree is empty. This can only occur if a tree
* is initially constructed with no arguments, or if we remove the
* only element from a tree.
*
* @author Michael Albert, Iain Hewson
*/
public class LinkedBST<T extends Comparable<T>> {
/** The element held at the root of this tree. */
private T root;
/** The left subtree of this tree. */
private LinkedBST<T> left;
/** The right subtree of this tree. */
private LinkedBST<T> right;
/**
* Creates a BST with the given value.
*
* @param value to store at the root of this LinkedBST.
*/
public LinkedBST(T value) {
root = value;
left = null;
right = null;
}
/**
* Creates a new empty BST.
*/
public LinkedBST() {
this(null);
}
/**
* Adds an element to this BST if it isn't already there.
*
* @param element an element to be added.
*/
public void add(T element) {
if (root == null) {
root = element;
}
int comparison = root.compareTo(element);
if (comparison > 0) {
if (left == null) {
left = new LinkedBST<T>(element);
} else {
left.add(element);
}
} else if (comparison < 0) {
if (right == null) {
right = new LinkedBST<T>(element);
} else {
right.add(element);
}
}
}
/**
* Returns the height of this tree.
*
* @return the height of this tree.
*/
public int height() {
int leftH = 0, rightH = 0;
if (root == null) {
return 0;
}
if (right != null) {
rightH = 1 + right.height();
}
if (left != null) {
leftH = 1 + left.height();
}
return Math.max(leftH, rightH);
}
/**
* Searches for the given target within this tree.
*
* @param target
* @return true if target is found, otherwise false.
*/
public boolean search(T target) {
boolean lefth = false, righth = false;
if (root == null) {
return false;
}
int comparison = root.compareTo(target);
if (comparison == 0) {
return true;
}
if (comparison > 0) {
if (left != null) {
lefth = left.search(target);
}
return lefth;
}
if (comparison < 0) {
if (right != null) {
righth = right.search(target);
}
return righth;
}
return false;
}
/**
* Returns the size of this BST.
*
* @return the size of this BST.
*/
public int size() {
int lefth = 0, righth = 0;
if (root == null) {
return 0;
}
if (right != null) {
righth = right.size();
}
if (left != null) {
lefth = left.size();
}
return 1 + lefth + righth;
}
/**
* Returns how many elements are greater than or equal to the
* parameter <code>low</code>.
*
* @param low the lower bound to use when counting elements.
* @return how many elements are greater than or equal to the
* parameter <code>low</code>.
*/
public int sizeAbove(T low) {
if (root == null) {
return 0;
}
return 0;
}
/**
* Returns how many elements are less than the parameter
* <code>high</code>.
*
* @param high the element to compare when counting elements.
* @return how many elements are less than the parameter
* <code>high</code>.
*/
public int sizeBelow(T high) {
// implement this for part 2
return 0;
}
/**
* Returns how many elements are greater than or equal to the
* parameter <code>low</code> and less than the parameter
* <code>high</code>.
*
* @param low the lower bound to use when counting elements.
* @param high the upper bound to use when counting elements.
* @return how many elements are between low (inclusive) and
* high (exclusive).
*/
public int sizeBetween(T low, T high) {
// implement this for part 2
return 0;
}
/**
* Removes the given element from this tree if it is present.
*
* @param element the element to remove.
*/
public void remove(T element) {
// implement this method from the lectures if you
// want to do the extension exercises
}
/** The direction used when creating a representation of this tree. */
enum Direction {LEFT, RIGHT, NO};
/**
* Recursively generates a representation of this tree.
*
* @param curr the current line being generated.
* @param dir the direction of the last link followed.
* @param result the representation generated so far.
* @return a representation of this tree.
*/
public StringBuilder str(String curr, Direction dir, StringBuilder result) {
if(right != null) {
right.str(curr + (dir == LEFT ? "│ " : " "), RIGHT, result);
}
if (root != null) {
result.append(curr + (dir == RIGHT ? "┌─ " :
dir == LEFT ? "└─ " : " ") + root + "\n");
}
if(left != null) {
left.str(curr + (dir == RIGHT ? "│ " : " "), LEFT, result);
}
return result;
}
@Override
public String toString() {
return str("", NO, new StringBuilder()).toString();
}
/**
* Entry point of program (used for testing).
* Valid commands are:
* <pre>
* a (add) item(s) - calls add with each item
* f (find) item - calls search with item
* p (print) - calls toString
* h (height) - calls height
* s (size) - calls size
* sa (sizeabove) low - calls sizeAbove(low)
* sb (sizebelow) high - calls sizeBelow(high)
* si (sizeinbetween) low high - calls sizeBetween(low,high)
* </pre>
* Return values of methods are printed to stdout.
*
* @param args command line arguments are not used.
*/
public static void main(String[] args) {
LinkedBST<String> tree = new LinkedBST<>();
Scanner input = new Scanner(System.in);
while (input.hasNextLine()) {
Scanner line = new Scanner(input.nextLine());
if (line.hasNext()) {
String command = line.next();
switch (command) {
case "a": case "add":
while (line.hasNext()) {
tree.add(line.next());
}
break;
case "f": case "find":
if (line.hasNext()) {
System.out.println(tree.search(line.next()));
}
break;
case "p": case "print":
System.out.print(tree);
break;
case "h": case "height":
System.out.println(tree.height());
break;
case "s": case "size":
System.out.println(tree.size());
break;
case "sa": case "sizeabove":
if (line.hasNext()) {
String low = line.next();
System.out.println(tree.sizeAbove(low));
}
break;
case "sb": case "sizebelow":
if (line.hasNext()) {
System.out.println(tree.sizeBelow(line.next()));
}
break;
case "si": case "sizeinbetween":
if (line.hasNext()) {
String low = line.next();
if (line.hasNext()) {
System.out.println(tree.sizeBetween
(low, line.next()));
}
}
break;
default:
System.err.println("Unknown command: " + command);
}
}
}
}
}
System.out.println(tree.sizeBelow(line.next()));
}
break;
case "si": case "sizeinbetween":
if (line.hasNext()) {
String low = line.next();
if (line.hasNext()) {
System.out.println(tree.sizeBetween
(low, line.next()));
}
}
break;
default:
System.err.println("Unknown command: " + command);
}
}
}
}
}
答案 0 :(得分：1)
由于这是家庭作业，我会尽力指出你正确的方向，而不是为你做。手头的任务可以通过递归更好地解决，当涉及到二叉树时，有几种不同类型的遍历可以递归完成。
如果我们发现任何低于high的值，我会执行有序遍历并相应增加。
提示：
你需要创建一个inOrder方法，该方法接受root的参数和T high的参数，并递归遍历树，检查当前节点值是否小于high。
public int sizeBelow(T high) {
// return inOrder(root,high);
}
private int inOrder(type current, type high){
// check if ANY of root or high are null (if yes return 0)
// recursively go down the tree comparing current against high
// if current is less than high then return 1 + inOrder(...,high)
// all other conditions should return 0.
}
确保您阅读Tree Traversals (Inorder, Preorder and Postorder)。当您点击此链接时，请确保选择JAVA标签，因为默认情况下，示例会显示在C中。