Validate Binary Search Tree

描述

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.

    分析

无

代码

  1. // Validate Binary Search Tree
  2. // 时间复杂度O(n)，空间复杂度O(\logn)
  3. public class Solution {
  4.     public boolean isValidBST(TreeNode root) {
  5.         return isValidBST(root, INT_MIN, INT_MAX);
  6.     }
  8.     bool isValidBST(TreeNode* root, int lower, int upper) {
  9.         if (root == nullptr) return true;
  11.         return root.val > lower && root.val < upper
  12.                 && isValidBST(root.left, lower, root.val)
  13.                 && isValidBST(root.right, root.val, upper);
  14.     }
  15. }

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原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/java/binary-tree/bst/validate-binary-search-tree.html