二叉树的递归套路——搜索二叉树

package com.harrison.class08;
import java.util.ArrayList;
public class Code06_IsBST {
  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 boolean isBST;
    public int max;
    public int min;
    public Info(boolean is,int ma,int mi) {
      isBST=is;
      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);
    int max=head.value;
    int min=head.value;
    if(leftInfo!=null) {
      max=Math.max(max, leftInfo.max);
      min=Math.min(min, leftInfo.min);
    }
    if(rightInfo!=null) {
      max=Math.max(max, rightInfo.max);
      min=Math.min(min, rightInfo.min);
    }
    boolean isBST=false;
    if(
      (leftInfo==null?true:leftInfo.isBST)
      &&
      (rightInfo==null?true:rightInfo.isBST)
      &&
      (leftInfo==null?true:leftInfo.max<head.value)
      &&
      (rightInfo==null?true:rightInfo.min>head.value)
      ) {
      isBST=true;
    }
    return new Info(isBST, max, min);
  }
  public static boolean isBST1(Node head) {
    if(head==null) {
      return true;
    }
    return process1(head).isBST;
  }
  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 boolean isBST2(Node head) {
    if (head == null) {
      return true;
    }
    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 false;
      }
    }
    return true;
  }
  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 (isBST1(head) != isBST2(head)) {
        System.out.println("Oops!");
      }
    }
    System.out.println("finish!");
  }
}