Validate Binary Search Tree

最新推荐文章于 2024-10-14 16:31:29 发布

最新推荐文章于 2024-10-14 16:31:29 发布 · 65 阅读

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本文介绍了一种检查给定二叉树是否为有效二叉搜索树的方法。通过递归遍历节点并利用ArrayList来记录节点值，确保左子树的所有节点值小于根节点而右子树的所有节点值大于根节点，同时左右子树也必须符合二叉搜索树的定义。

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.

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isValidBST(TreeNode root) {
    	ArrayList<Integer> arrayList = new ArrayList<Integer>();
    	arrayList.add(null);
        return solve(root, arrayList);
    }

	private boolean solve(TreeNode root, ArrayList<Integer> arrayList) {
		if (root == null) {
			return true;
		}
		boolean left = solve(root.left, arrayList);
		if (arrayList.get(arrayList.size()-1) != null && root.val<=arrayList.get(arrayList.size()-1)) {
			return false;
		}
		arrayList.add(root.val);
		boolean right = solve(root.right, arrayList);
		return left && right;
	}

}