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面试题 04.05:合法二叉搜索树

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轩辕龙儿 2022-05-26 16:19:01 +08:00
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src/main/java/leetcode/editor/cn/LegalBinarySearchTreeLcci.java Normal file
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//<p>实现一个函数，检查一棵二叉树是否为二叉搜索树。</p><strong>示例 1:</strong><pre><strong>输入:</strong><br> 2<br> / &#92<br> 1 3<br><strong>输出:</strong> true<br></pre><strong>示例 2:</strong><pre><strong>输入:</strong><br> 5<br> / &#92<br> 1 4<br> / &#92<br> 3 6<br><strong>输出:</strong> false<br><strong>解释:</strong> 输入为: [5,1,4,null,null,3,6]。<br> 根节点的值为 5 ，但是其右子节点值为 4 。</pre><div><div>Related Topics</div><div><li>树</li><li>深度优先搜索</li><li>二叉搜索树</li><li>二叉树</li></div></div><br><div><li>👍 76</li><li>👎 0</li></div>
package leetcode.editor.cn;
import com.code.leet.entiy.TreeNode;
// 面试题 04.05:合法二叉搜索树
public class LegalBinarySearchTreeLcci {
public static void main(String[] args) {
Solution solution = new LegalBinarySearchTreeLcci().new Solution();
// TO TEST
}
//leetcode submit region begin(Prohibit modification and deletion)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean isValidBST(TreeNode root) {
return dfs(root, null, null);
}
public boolean dfs(TreeNode node, Integer lower, Integer upper) {
if (node == null) {
return true;
}
int val = node.val;
if (lower != null && val <= lower) {
return false;
}
if (upper != null && val >= upper) {
return false;
}
if (!dfs(node.right, val, upper)) {
return false;
}
return dfs(node.left, lower, val);
}
}
//leetcode submit region end(Prohibit modification and deletion)
}

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src/main/java/leetcode/editor/cn/doc/content/LegalBinarySearchTreeLcci.md Normal file
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<p>实现一个函数，检查一棵二叉树是否为二叉搜索树。</p><strong>示例 1:</strong><pre><strong>输入:</strong><br> 2<br> / &#92<br> 1 3<br><strong>输出:</strong> true<br></pre><strong>示例 2:</strong><pre><strong>输入:</strong><br> 5<br> / &#92<br> 1 4<br>  / &#92<br>  3 6<br><strong>输出:</strong> false<br><strong>解释:</strong> 输入为: [5,1,4,null,null,3,6]。<br>  根节点的值为 5 ，但是其右子节点值为 4 。</pre><div><div>Related Topics</div><div><li>树</li><li>深度优先搜索</li><li>二叉搜索树</li><li>二叉树</li></div></div><br><div><li>👍 76</li><li>👎 0</li></div>