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Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-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L0→Ln→L1→L2→L3→，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;
}
}
Java for LeetCode 143 Reorder List
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原文地址：http://www.cnblogs.com/tonyluis/p/4552949.html
