98. Validate Binary Search Tree
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98. Validate Binary Search Tree
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
- The left subtree of a node contains only nodes with keys less than the node's key.
- The right subtree of a node contains only nodes with keys greater than the node's key.
- Both the left and right subtrees must also be binary search trees.
Example 1:
2 / \ 1 3Binary tree
[2,1,3]
, return true.Example 2:
1 / \ 2 3Binary tree
[1,2,3]
, return false.原题链接 讨论解题链接
根据中序遍历,如果BST是有效的,则中序结果是递增的。
一种方法是用一个引用pre记录当前节点在中序遍历情况下的前一个节点,保证pre要小于当前的节点。
另一种方法是设置范围lower和upper,每个节点都要在这一范围, 它在每次遍历的时候都会更新,如node->val是它的左节点的上限,是它右节点的下限。
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- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
- 98. Validate Binary Search Tree
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