验证二叉搜索树

function isValide(root, min, max) {
    if (root === null) return true;
    if (min != null && root.val <= min) return false;
    if (max != null && root.val >= max) return false;
    return isValide(root.left, min, root.val) && isValide(root.right, root.val, max);
}
var isValidBST = function(root) {
    return isValide(root, -Infinity, Infinity);
};

var isValidBST = function(root) {
    let stack = [];
    let inorder = -Infinity;
    while (stack.length || root !== null) {
        while (root !== null) {
            stack.push(root);
            root = root.left;
        }
        root = stack.pop();
        // 如果中序遍历得到的节点的值小于等于前一个 inorder，说明不是二叉搜索树
        if (root.val <= inorder) {
            return false;
        }
        inorder = root.val;
        root = root.right;
    }
    return true;
};