[JS]链表倒数第k个节点

常规解法，快指针向前遍历k个

function FindKthToTail(head, k)
{
    // write code here

    let fast = head
    let i=0
    for(;i<k&&fast;i++){

        fast = fast.next
    }
    if(!fast&&i<k){
        return //k比链表的长度还大
    }

    while(fast){
        head = head.next
        fast = fast.next
    }

    return head
}