二叉树的递归套路——最大二叉搜索子树头结点

public static class Info{
    public Node maxSubBSTHead;
    //public boolean isAllBST;
    public int maxSubBSTSize;
    public int max;
    public int min;
    public Info(Node h,int size,int ma,int mi) {
      maxSubBSTHead=h;
      maxSubBSTSize=size;
      max=ma;
      min=mi;
    }
  }

package com.harrison.class08;
import java.util.ArrayList;
public class Code07_MaxSubBSTHead {
  public static class Node {
    public int value;
    public Node left;
    public Node right;
    public Node(int data) {
      this.value = data;
    }
  }
  public static class Info{
    public Node maxSubBSTHead;
    public int maxSubBSTSize;
    public int max;
    public int min;
    public Info(Node h,int size,int ma,int mi) {
      maxSubBSTHead=h;
      maxSubBSTSize=size;
      max=ma;
      min=mi;
    }
  }
  public static Info process1(Node head) {
    if(head==null) {
      return null;
    }
    Info leftInfo=process1(head.left);
    Info rightInfo=process1(head.right);
    Node maxSubBSTHead=null;
    int maxSubBSTSize=0;
    int max=head.value;
    int min=head.value;
    if(leftInfo!=null) {
      max=Math.max(max, leftInfo.max);
      min=Math.min(min, leftInfo.min);
      maxSubBSTHead=leftInfo.maxSubBSTHead;
      maxSubBSTSize=leftInfo.maxSubBSTSize;
    }
    if(rightInfo!=null) {
      max=Math.max(max, rightInfo.max);
      min=Math.min(min, rightInfo.min);
      if(rightInfo.maxSubBSTSize>maxSubBSTSize) {
        maxSubBSTSize=rightInfo.maxSubBSTSize;
        maxSubBSTHead=rightInfo.maxSubBSTHead;
      }
    }
    // 如果在一棵子树上，最大二叉搜索子树的头节点就是子树的头节点，意味着整颗子树就是搜索二叉树
    if(
      (leftInfo==null?true:(leftInfo.maxSubBSTHead==head.left))
      &&
      (rightInfo==null?true:(rightInfo.maxSubBSTHead==head.right))
      &&
      (leftInfo==null?true:leftInfo.max<head.value)
      &&
      (rightInfo==null?true:rightInfo.min>head.value)
      ) {
      maxSubBSTHead=head;
      maxSubBSTSize=(
              (leftInfo==null?0:leftInfo.maxSubBSTSize)
              +
              (rightInfo==null?0:rightInfo.maxSubBSTSize)
              +1
                );
    }
    return new Info(maxSubBSTHead, maxSubBSTSize, max, min);
  }
  public static Node maxSubBSTHead1(Node head) {
    if(head==null) {
      return null;
    }
    return process1(head).maxSubBSTHead;
  }
  public static int getBSTSize(Node head) {
    if (head == null) {
      return 0;
    }
    ArrayList<Node> arr = new ArrayList<>();
    in(head, arr);
    for (int i = 1; i < arr.size(); i++) {
      if (arr.get(i).value <= arr.get(i - 1).value) {
        return 0;
      }
    }
    return arr.size();
  }
  public static void in(Node head, ArrayList<Node> arr) {
    if (head == null) {
      return;
    }
    in(head.left, arr);
    arr.add(head);
    in(head.right, arr);
  }
  public static Node maxSubBSTHead2(Node head) {
    if (head == null) {
      return null;
    }
    if (getBSTSize(head) != 0) {
      return head;
    }
    Node leftAns = maxSubBSTHead1(head.left);
    Node rightAns = maxSubBSTHead1(head.right);
    return getBSTSize(leftAns) >= getBSTSize(rightAns) ? leftAns : rightAns;
  }
  public static Node generateRandomBST(int maxLevel, int maxValue) {
    return generate(1, maxLevel, maxValue);
  }
  public static Node generate(int level, int maxLevel, int maxValue) {
    if (level > maxLevel || Math.random() < 0.5) {
      return null;
    }
    Node head = new Node((int) (Math.random() * maxValue));
    head.left = generate(level + 1, maxLevel, maxValue);
    head.right = generate(level + 1, maxLevel, maxValue);
    return head;
  }
  public static void main(String[] args) {
    int maxLevel = 4;
    int maxValue = 100;
    int testTimes = 1000000;
    for (int i = 0; i < testTimes; i++) {
      Node head = generateRandomBST(maxLevel, maxValue);
      if (maxSubBSTHead1(head) != maxSubBSTHead2(head)) {
        System.out.println("Oops!");
      }
    }
    System.out.println("finish!");
  }
}