1.在二叉搜索树中，查找任意两个节点的最近公共父节点
public > TreeNode getFather(TreeNode root,TreeNode p,TreeNode q){
if(root==null|| p.equals(root)|| q.equals(root)){
return root;
}
if(root.value.compareTo(p.value)>0 && root.value.compareTo(q.value)>0){
TreeNode left=getFather(root.left,p,q);
return left;
}
if(root.value.compareTo(p.value)<0 && root.value.compareTo(q.value)<0){
TreeNode right=getFather(root.right,p,q);
return right;
}
return root;
}
2.在二叉查找树中寻找两个节点，使它们的和为一个给定值
image.png
public boolean findTarget(TreeNode root,Integer target){
List list=new ArrayList<>();
inOrder(root,list);
int left=0;
int right=list.size()-1;
while(left node1=list.get(left);
TreeNode node2=list.get(right);
if(node1.value+node2.value==target){
return true;
}
else if(node1.value+node2.value>target){
right=right-1;
}
else{
left=left+1;
}
}
return false;
}
public void inOrder(TreeNode root,List list){
if(root==null){
return;
}
inOrder(root.left,list);
list.add(root);
inOrder(root.right,list);
}
3.Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.
Note:
You may assume k is always valid, 1 ≤ k ≤ BST's total elements.
image.png
辅助类
public class Holder {
boolean flag=false;
}
private T value;
int count=0;//count为啥不能作为参数传进去
/*
*
*/
/*
* 寻找二叉查找树的第 k 个元素
*/
public T getK(TreeNode root,int k){
///boolean flag=false;
Holder holder=new Holder();
inOrderTraversal(root,k,holder);
return value;
}
public void inOrderTraversal(TreeNode root,int k,Holder holder){
if(holder.flag==true){
return;
}
if(root== null){
return;
}
inOrderTraversal(root.left,k,holder);
count++;
if(count==k){
value= root.value;
holder.flag=true;
//return;
}
//System.out.println(count+"."+root.value+holder.flag);
inOrderTraversal(root.right, k,holder);
}
4.二叉搜索树中一个节点的前驱(找二叉树中一个节点的前驱，算法和这个一样)
TreeNode pre;
private T preValue;
private int preCnt;
public T getPreElement(TreeNode root,TreeNode p){
inOrderTraversalPre(root,p);
return preValue;
}
public void inOrderTraversalPre(TreeNode root,TreeNode node){
if(root== null){
return;
}
inOrderTraversalPre(root.left,node);
preCnt++;
if(preCnt==1){
preValue=null;
pre=root;
}
//System.out.println(preCnt+"."+root.value);
else{
if(!root.value.equals(node.value)){
pre=root;
}
if(root.value.equals(node.value)){
preValue=pre.value;
}
}
inOrderTraversalPre(root.right, node);
}
5.二叉搜索树中一个节点的后继(找二叉树中一个节点的后继，算法和这个一样)
int postCnt=0;
private int temp;
private T postValue;
/**
*
* @param root
* @param p
* @return
*Description: 查找指定元素的后继
*/
public T getPostElement(TreeNode root,TreeNode p){
Holder holder=new Holder();
inOrderTraversal(root,p,holder);
return postValue;
}
public void inOrderTraversal(TreeNode root,TreeNode node,Holder holder){
if(holder.flag==true){
return;
}
if(root== null){
return;
}
inOrderTraversal(root.left,node,holder);
postCnt++;
//System.out.println(postCnt+"."+root.value+holder.flag);
if(root.value.equals(node.value)){
temp=postCnt;
}
if(postCnt==temp+1){
postValue=root.value;
holder.flag=true;
}
inOrderTraversal(root.right, node,holder);
}
6.从有序链表中构造二叉搜索树
快慢指针找链表的中间位置
/**
*
* @param head
* @return
*Description:找有序链表的中间位置的前驱
*/
public MyNode getPreOfMid(MyNode head){
MyNode fast=head;
MyNode slow=head;
MyNode pre=head;
while(fast!=null && fast.getNext()!=null){
pre=slow;
slow=slow.getNext();
fast=fast.getNext().getNext();
}
//System.out.println(slow.getData());
return pre;
}
构造二叉搜索树
public TreeNode sortedListToBST(MyNode head) {
if(head==null){
return null;
}
if(head.getNext()==null){
return new TreeNode(head.getData());
}
MyNode pre=getPreOfMid(head);
MyNode mid=pre.getNext();
pre.setNext(null);//断开链表
TreeNode root=new TreeNode(mid.getData());
root.left=sortedListToBST(head);
root.right=sortedListToBST(mid.getNext());
return root;
}