remove-nth-node-from-end-of-list.js

/**Given the head of a linked list, remove the nth node from the end of the list and return its head. */
/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} n
 * @return {ListNode}
 */
 var removeNthFromEnd = function(head, n) {
    let p1 = head
    while (p1 && n--) {
      p1 = p1.next
    }
  
    if (!p1) { return n ? head : head.next }
  
    let p2 = head
    while (p1.next) {
      p1 = p1.next
      p2 = p2.next
    }
  
    p2.next = p2.next.next
  
    return head
  };