ValidBinarySearchTree
ValidBinarySearchTree.java 源码
package algorithm.recursion;
/**
* @author roseduan
* @time 2020/9/23 8:11 下午
* @description 验证二叉搜索树
*/
public class ValidBinarySearchTree {
/**
* 根据二叉搜索树的特征，递归
*/
public boolean isValidBST(TreeNode root) {
return helper(root, Long.MIN_VALUE, Long.MAX_VALUE);
}
private boolean helper(TreeNode node, long min, long max) {
if (node == null) {
return true;
}
if (node.val <= min || node.val >= max) {
return false;
}
return helper(node.left, min, node.val) && helper(node.right, node.val, max);
}
/**
* 中序遍历
*/
private TreeNode prev = null;
public boolean isValidBST2(TreeNode root) {
if (root == null) {
return true;
}
if (!isValidBST2(root.left)) {
return false;
}
if (prev != null && prev.val >= root.val) {
return false;
}
prev = root;
return isValidBST2(root.right);
}
public static class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int val) { this.val = val; }
TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
}
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