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  • Java for LeetCode 143 Reorder List

    Given a singly linked list L: L0L1→…→Ln-1Ln,
    reorder it to: L0LnL1Ln-1L2Ln-2→…

    You must do this in-place without altering the nodes' values.

    For example,
    Given {1,2,3,4}, reorder it to {1,4,2,3}.

    解题思路一:

    每次将Ln换到前面,得到L0LnL1L2L3→,然后对L1使用相同操作,JAVA实现如下:

    	public void reorderList(ListNode head) {
    		ListNode headCopy = head;
    		while (headCopy != null && headCopy.next != null
    				&& headCopy.next.next != null) {
    			ListNode temp = headCopy;
    			while (temp.next.next != null)
    				temp = temp.next;
    			temp.next.next = headCopy.next;
    			headCopy.next = temp.next;
    			temp.next = null;
    			temp = headCopy.next.next;
    			headCopy=headCopy.next.next;
    		}
    	}
    

     结果TLE

    解题思路二:

    空间换时间,将所有的node存到一个list中,然后每次操作list头尾两个node即可,JAVA实现如下:

        public void reorderList(ListNode head) {
    		LinkedList<ListNode> list = new LinkedList<ListNode>();
    		ListNode headCopy = head,end = head;
    		while (headCopy != null) {
    			list.add(headCopy);
    			headCopy = headCopy.next;
    		}
    		while(list.size()>2){
    			headCopy=list.poll();
    			end=list.get(list.size()-1);
    			list.remove(list.size()-1);
    			headCopy.next=end;
    			end.next=list.peek();
    			list.get(list.size()-1).next=null;
    		}
        }
    
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  • 原文地址:https://www.cnblogs.com/tonyluis/p/4552949.html
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