Largest BST Subtree
2016-08-03 07:27
351 查看
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.
Here's an example:
The Largest BST Subtree in this case is the highlighted one.
The return value is the subtree's size, which is 3.
思路:buttom-up,自底向上传递信息,一个是min,一个max,另外一个是是否是bst,result的信息用一个array来保存,这样在遍历整个树的过程中,已经更新了valid bst的个数。这样就是O(n)的复杂度。记住初始值用Long型表达,防止溢出。首先明白了需要自底向上传递信息,那么肯定要建立一个新的数据结构来表达这种信息,然后要明白的是,traverse这个tree还是用原来的TreeNode,但是返回的信息,是自己定义的,就跟int boolean一个道理,所以,这个建立的node跟原来的TreeNode是两个不相关的概念。每走一层,就是建立一个这样的信息节点,然后往上返回。同时,更新res
array的信息。这样最后我可以搜刮到关于这个树的信息。也就是最大的BST node数目。
Note:
A subtree must include all of its descendants.
Here's an example:
10 / \ 5 15 / \ \ 1 8 7
The Largest BST Subtree in this case is the highlighted one.
The return value is the subtree's size, which is 3.
思路:buttom-up,自底向上传递信息,一个是min,一个max,另外一个是是否是bst,result的信息用一个array来保存,这样在遍历整个树的过程中,已经更新了valid bst的个数。这样就是O(n)的复杂度。记住初始值用Long型表达,防止溢出。首先明白了需要自底向上传递信息,那么肯定要建立一个新的数据结构来表达这种信息,然后要明白的是,traverse这个tree还是用原来的TreeNode,但是返回的信息,是自己定义的,就跟int boolean一个道理,所以,这个建立的node跟原来的TreeNode是两个不相关的概念。每走一层,就是建立一个这样的信息节点,然后往上返回。同时,更新res
array的信息。这样最后我可以搜刮到关于这个树的信息。也就是最大的BST node数目。
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public int largestBSTSubtree(TreeNode root) { if(root == null) return 0; int[] res = {0}; collect(root, res); return res[0]; } public Node collect(TreeNode root, int[] res){ Node node = new Node(); if(root == null){ node.isBST = true; return node; } Node leftnode = collect(root.left, res); Node rightnode = collect(root.right, res); if(leftnode.isBST && leftnode.max < root.val && rightnode.isBST && root.val < rightnode.min){ node.isBST = true; node.min = Math.min(root.val, leftnode.min); node.max = Math.max(root.val, rightnode.max); node.size = leftnode.size + rightnode.size + 1; res[0] = Math.max(res[0], node.size); } return node; } class Node{ long min; long max; boolean isBST = false; int size; public Node(){ min = Long.MAX_VALUE; max = Long.MIN_VALUE; size = 0; } } }
相关文章推荐
- LeetCode-Largest BST Subtree
- LeetCode "Largest BST Subtree"
- largestBSTSubtree
- LeetCode Largest BST Subtree
- Leetcode: Largest BST Subtree
- [LeetCode] Largest BST Subtree 最大的二分搜索子树
- [Locked] Largest BST Subtree
- Largest Subtree Which is a Binary Search Tree (BST)
- Largest BST Subtree
- 333. Largest BST Subtree
- Largest BST Subtree
- Medium 333题 Largest BST Subtree
- [leetcode] 333. Largest BST Subtree 解题报告
- [Leetcode] 333. Largest BST Subtree 解题报告
- LeetCode 333. Largest BST Subtree
- leetcode 333. Largest BST Subtree
- 333. Largest BST Subtree
- 333. Largest BST Subtree
- 333. Largest BST Subtree
- Largest BST in a Binary Tree