资讯专栏INFORMATION COLUMN

[LeetCode] 333. Largest BST Subtree

tigerZH / 2235人阅读

Problem

Given a binary tree, find the largest subtree which is a Binary Search Tree (BST), where largest means subtree with largest number of nodes in it.

Note:
A subtree must include all of its descendants.

Example:

Input: [10,5,15,1,8,null,7]

   10 
   /  
  5  15 
 /     
1   8   7

Output: 3
Explanation: The Largest BST Subtree in this case is the highlighted one.
             The return value is the subtree"s size, which is 3.

Follow up:
Can you figure out ways to solve it with O(n) time complexity?

Solution

First try:

class Solution {
    public int largestBSTSubtree(TreeNode root) {
        if (root == null) return 0;
        if (isBST(root)) return largestBSTSubtree(root.left)+largestBSTSubtree(root.right)+1;
        return Math.max(largestBSTSubtree(root.left), largestBSTSubtree(root.right));
    }
    private boolean isBST(TreeNode root) {
        if (root == null) return true;
        if (root.left != null && findMax(root.left) >= root.val) return false;
        if (root.right != null && findMin(root.right) <= root.val) return false;
        if (isBST(root.left) && isBST(root.right)) return true;
        return false;
    }
    private int findMax(TreeNode root) {
        while (root.right != null) root = root.right;
        return root.val;
    }
    private int findMin(TreeNode root) {
        while (root.left != null) root = root.left;
        return root.val;
    }
}

Optimized:

class Solution {
    public int largestBSTSubtree(TreeNode root) {
        if (root == null) return 0;
        if (isBST(root, null, null)) return largestBSTSubtree(root.left)+largestBSTSubtree(root.right)+1;
        return Math.max(largestBSTSubtree(root.left), largestBSTSubtree(root.right));
    }
    private boolean isBST(TreeNode root, Integer min, Integer max) {
        if (root == null) return true;
        if (min != null && min >= root.val) return false;
        if (max != null && max <= root.val) return false;
        if (isBST(root.left, min, root.val) && isBST(root.right, root.val, max)) return true;
        return false;
    }
}

文章版权归作者所有,未经允许请勿转载,若此文章存在违规行为,您可以联系管理员删除。

转载请注明本文地址:https://www.ucloud.cn/yun/72038.html

相关文章

  • LeetCode[333] Largest BST Subtree

    摘要:复杂度思路考虑对于每一个节点来说,能组成的的。那么并且所以我们需要两个返回值,一个是这个是不是,另一个是当前的能组成的最大的值。代码这个能构成一个这个不能构成一个 LeetCode[333] Largest BST Subtree Given a binary tree, find the largest subtree which is a Binary SearchTree (B...

    WrBug 评论0 收藏0
  • [LeetCode] Largest BST Subtree

    Largest BST Subtree Given a binary tree, find the largest subtree which is a Binary Search Tree (BST), where largest means subtree with largest number of nodes in it. Note: A subtree must include all ...

    Youngdze 评论0 收藏0
  • 333. Largest BST Subtree

    10 / 5 15 / 1 8 7 return 3 public class Solution { public int largestBSTSubtree(TreeNode root) { if(root == null) return 0; int[] res = recursive(root); ...

    DataPipeline 评论0 收藏0
  • [LeetCode] 776. Split BST

    Problem Given a Binary Search Tree (BST) with root node root, and a target value V, split the tree into two subtrees where one subtree has nodes that are all smaller or equal to the target value, whil...

    baiy 评论0 收藏0
  • [LeetCode] 501. Find Mode in Binary Search Tree

    Problem Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST. Assume a BST is defined as follows: The left subtree of a node c...

    NikoManiac 评论0 收藏0

发表评论

0条评论

最新活动
阅读需要支付1元查看
<