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package Tree;

/**

* 判断是否为二叉排序树，每次记录前一个数，判断当前是否大于，如果不是，则不为二叉排序树

*/

public class ValidateBinarySearchTree_98 {

private long min=Long.MIN_VALUE;

public boolean isValidBST(TreeNode root) {

if(root==null) {

return true;

}

boolean left=isValidBST(root.left);

if(root.val<=min){

return false;

}

min=root.val;

boolean right=isValidBST(root.right);

return left&&right;

}

class TreeNode {

int val;

TreeNode left;

TreeNode right;

TreeNode() {}

TreeNode(int val) { this.val = val; }

TreeNode(int val, TreeNode left, TreeNode right) {

this.val = val;

this.left = left;

this.right = right;

}

}

}