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[英]By using this BST insertion method I have only root as output,why?
[英]Why is the recursive insertion method of the BST not working
我编写了以下代码,以实现BST的递归插入方法。 但是,当我按遍历顺序打印树时,它会在插入之前打印原始树。 好像没有插入元素。 请帮帮我。 提前致谢。 还请提出更改代码的建议。 顺便说一下,遍历顺序中的初始树是2 5 5 6 7 8。
package DataStructures;
class TreeNode {
private TreeNode parent;
private TreeNode childLeft;
private TreeNode childRight;
private int key;
public TreeNode(){
}
public TreeNode(int key) {
this(key, null);
}
public TreeNode(int key, TreeNode parent) {
this(key, parent, null, null);
}
public TreeNode(int key, TreeNode parent, TreeNode childLeft, TreeNode childRight) {
this.key = key;
this.parent = parent;
this.childLeft = childLeft;
this.childRight = childRight;
}
public int getKey() {
return key;
}
public void setKey(int key) {
this.key = key;
}
public TreeNode getParent() {
return parent;
}
public void setParent(TreeNode parent) {
this.parent = parent;
}
public TreeNode getChildLeft() {
return childLeft;
}
public void setChildLeft(TreeNode childLeft) {
this.childLeft = childLeft;
}
public TreeNode getChildRight() {
return childRight;
}
public void setChildRight(TreeNode childRight) {
this.childRight = childRight;
}
}
public class BinarySearchTreeBasicTest {
private static class BinarySearchTree {
private TreeNode root;
private TreeNode maxNode = new TreeNode(0);
public BinarySearchTree(TreeNode root) {
this.root = root;
}
public void printTheTreeInOrderWalk(TreeNode x) {
if (x != null) {
printTheTreeInOrderWalk(x.getChildLeft());
System.out.print(x.getKey() + " ");
printTheTreeInOrderWalk(x.getChildRight());
}
}
public void insertNode(TreeNode node, int key){
if (node == null){
node = new TreeNode(key);
}
else{
if (node.getKey() > key){
insertNode(node.getChildLeft(), key);
} else if (node.getKey() < key){
System.out.println("k");
insertNode(node.getChildRight(), key);
} else{
// dont do anything
}
}
}
}
public static void main(String[] args) {
TreeNode rootNode = new TreeNode(6);
BinarySearchTree tree = new BinarySearchTree(rootNode);
TreeNode node1 = new TreeNode(5);
TreeNode node2 = new TreeNode(7);
rootNode.setChildLeft(node1);
rootNode.setChildRight(node2);
node1.setParent(rootNode);
node2.setParent(rootNode);
TreeNode node3 = new TreeNode(2);
TreeNode node4 = new TreeNode(5);
node1.setChildLeft(node3);
node1.setChildRight(node4);
node3.setParent(node1);
node4.setParent(node1);
TreeNode node5 = new TreeNode(8);
node5.setParent(node2);
node2.setChildRight(node5);
tree.insertNode(rootNode, 3);
tree.printTheTreeInOrderWalk(rootNode);
}
}
在您的insertNode()
方法中,您只是在创建一个新节点。 您永远不会将新创建的节点添加到其父节点。 您应该检查是否要在此处插入,或者应该返回新返回的节点并进行相应的设置。
如果您不希望与当前程序有太大差异,可以进行以下更改。
public void insertNode(TreeNode node, int key) {
if (node.getKey() > key) {
if (node.left == null) { //check if you want to insert the node here
TreeNode newNode = new TreeNode(key);
node.left = newNode;
} else {
insertNode(node.getChildLeft(), key);
}
} else if (node.getKey() < key) {
if(node.right == null){ //check if you want to insert the node here
TreeNode newNode = new TreeNode(key);
node.right = newNode;
} else {
insertNode(node.getChildRight(), key);
}
} else {
// don't do anything
}
}
在Java中,参数是通过值传递的。 在insertNode
,如果您对node
不执行任何其他操作,则行node = new TreeNode(key);
insertNode
不会做任何有用的事情。
在树中插入的典型实现通过返回将替换前一个节点的TreeNode
来工作:
private TreeNode insertNode(TreeNode node, int key){
if (node == null){
node = new TreeNode(key);
}
else{
if (node.getKey() > key){
node.setChildLeft(insertNode(node.getChildLeft(), key));
} else if (node.getKey() < key){
node.setChildRight(insertNode(node.getChildRight(), key));
} else{
// dont do anything
}
}
return node;
}
再进一步,以前的方法实际上应该是private
。 public
方法应如下所示:
public void insertNode(int key){
root = insertNode(root, key);
}
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