[LeetCode 98] Validate Binary Search Tree

题目链接：validate-binary-search-tree

	//验证是否为二叉排序树
/**
 * 
		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.
 *
 */

public class ValidateBinarySearchTree {
	public class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;

		TreeNode(int x) {
			val = x;
		}
	}
	
//	74 / 74 test cases passed.
//	Status: Accepted
//	Runtime: 292 ms
//	Submitted: 0 minutes ago

    public boolean isValidBST(TreeNode root) {      
       return isValidBST(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
    }
    
    public boolean isValidBST(TreeNode root, int min, int max) {
    	if(root == null) return true;
    	boolean l = true;
    	boolean r = true;
    	if(root.val >= min && root.val <= max) {		//	min <= root.val <= max
    		if(root.val != Integer.MIN_VALUE) 
    			l = isValidBST(root.left, min, root.val - 1);
    		else {// 当root.val = Integer.MIN_VALUE时
				if(root.left != null) l = false;		//如果还有左节点，则不是二叉排序树		
			}
    		
    		if(root.val != Integer.MAX_VALUE)
    			r = isValidBST(root.right, root.val + 1, max);
    		else {// 当root.val = Integer.MAX_VALUE时
				if(root.right != null) l = false;		//如果还有右节点，则不是二叉排序树		
			}
    		return l && r;
    	}
    	else return false;				
    }
	public static void main(String[] args) {
		// TODO Auto-generated method stub

	}

}

[LeetCode 98] Validate Binary Search Tree

原文：http://blog.csdn.net/ever223/article/details/44560345