验证二叉搜索树

1. 递归+判断数组是否升序

var isValidBST = function(root) {// 搜索二叉树中序遍历之后的结果数组一定是升序if(!root){return true;}let result = [];var dg = function(node){if(node){dg(node.left);result.push(node.val);dg(node.right);}}dg(root);for(let i = 1; i < result.length; i++){if(result[i-1] >= result[i]){return false;}}return true;
};

2. 递归

var isValidBST = function(root) {if(!root){return true;}var dg = function(node,min,max){// 遍历到叶子节点if(!node){return true;}// 判断左子树上所有节点的值是否均小于它的根节点的值，右子树上所有节点的值是否均大于它的根节点的值if(node.val <= min || node.val >= max){return false;}return dg(node.left,min,node.val) && dg(node.right,node.val,max);}return dg(root,-Infinity, Infinity);
};