[98]验证二叉搜索树.java

//leetcode submit region begin(Prohibit modification and deletion)

/**
 * Definition for a binary tree node.
 * public 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;
 *     }
 * }
 */
class Solution {
	public boolean isValidBST(TreeNode root) {
		return isValidBST(root, null, null);
	}

	/* 限定以 root 为根的子树节点必须满足 max.val > root.val > min.val */
	boolean isValidBST(TreeNode root, TreeNode min, TreeNode max) {
		if (root == null) {
			return true;
		}
		
		if(min!= null && min.val >= root.val){
			return false;
		}
		
		if(max!=null && max.val<= root.val){
			return false;
		}
		
		return isValidBST(root.left,min,root)&& isValidBST(root.right,root,max);

	}
}
//leetcode submit region end(Prohibit modification and deletion)