链表

var hasCycle = function (head) {
 
    if (head === null) return false
    let fast = head
    let slow = head
    while (fast !== null && fast.next !== null) {
        fast = fast.next.next
        slow = slow.next
 
        if (fast === slow) return true
    }
    return false
};

var reversePrint = function (head) {
    const arr = []
 
    if (head === null) return arr
 
    let p = head
    while (p.next !== null) {
        arr.push(p.val)
        p = p.next
    }
    arr.push(p.val)
 
    return arr.reverse()
 
};