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Copy pathReverseLinkedList.java
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37 lines (31 loc) · 1.06 KB
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package LeetCode;
/***
* Leetcode no206
*/
public class ReverseLinkedList {
/***
* A -> B -> C
* C -> B -> A
*
* 思路：如果用Stack的话，Stack会长这样：A -> B -> C，
* 然后会pop C， B， A...
* 但是，因为是LinkList，所以可以用两个指针来省去Stack的储存空间:
* 1. 读一个element就按照这个element创一个ListNode
* 2. 按照逻辑，新建的这个ListNode是下一个ListNode的child
* 3. 所以两个指针分别是
* a) newHead = new ListNode(currHead.val)
* b) newHead.next = preHead
* c) preHead = newHead
*/
public ListNode solution(ListNode root) {
if (root == null || root.next == null) return root;
ListNode newHead = null, lastHead = null;
while(root != null) {
newHead = new ListNode(root.val);
newHead.next = lastHead;
lastHead = newHead;
root = root.next;
}
return newHead;
}
}