/*
 * function TreeNode(x) {
 *   this.val = x;
 *   this.left = null;
 *   this.right = null;
 * }
 */
/**
 * 代碼中的類名、方法名、參數(shù)名已經(jīng)指定，請勿修改，直接返回方法規(guī)定的值即可
 *
 * 
 * @param root TreeNode類 
 * @return bool布爾型
 */
function isValidBST( root ) {
    // write code here
    console.log(root)
    if (root === null) {
        return true
    }
    if (!root.left && !root.right) {
        return true
    }
    let left = root.left === null? -Infinity : root.left.val
    let right = root.right === null? Infinity : root.right.val
    let left_right = root.left.right === null? -Infinity : root.left.right.val
    if ((left < root.val) && (root.val< right) && (left_right < root.val)) {
        return isValidBST(root.left) && isValidBST(root.right)
    }
    else {
        return false
    }
}
module.exports = {
    isValidBST : isValidBST
};