【LeetCode】【19】【Remove Nth Node From End of List】【链表】

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题目：Given a linked list, remove the n-th node from the end of list and return its head.
解题思路：题目很简单，移除链表中的倒数第n个节点，先正序算一下链表长度，然后再找出第n个。善用dummy节点，可以用来删除第一个。
代码：

  class ListNode {
      int val;
      ListNode next;
      ListNode(int x) { val = x; }
  }
    public ListNode removeNthFromEnd(ListNode head, int n) {
        int num = 0;               //num代表链表长度
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode node = head;
        while (node!=null){
            num++;
            node = node.next;
        }

        node = dummy;
        int pre = num-n;           //倒数第n个节点的前驱位置
        while (pre>0){
            pre--;
            node = node.next;
        }
        node.next = node.next.next;          //删除第n个
        return dummy.next;
    }