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. class Solution {
  4. public:
  5.     bool isValidBST(TreeNode* root) {
  6.         return isValidBST(root, LONG_MIN, LONG_MAX);
  7.     }
  9.     bool isValidBST(TreeNode* root, long long lower, long long upper) {
  10.         if (root == nullptr) return true;
  12.         return root->val > lower && root->val < upper
  13.                 && isValidBST(root->left, lower, root->val)
  14.                 && isValidBST(root->right, root->val, upper);
  15.     }
  16. };

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