leetcode — reverse-linked-list
2024-10-19 04:23:12
/**
* Source : https://leetcode.com/problems/reverse-linked-list/
*
*
* Reverse a singly linked list.
*
* click to show more hints.
*
* Hint:
* A linked list can be reversed either iteratively or recursively. Could you implement both?
*/
public class ReverseLinkedList {
/**
*
* 反转单向链表
*
* 使用迭代的方法
*
* @param head
* @return
*/
public Node reverseByIterative (Node head) {
Node pre = null;
while (head != null) {
Node next = head.next;
head.next = pre;
pre = head;
head = next;
}
return pre;
}
/**
* 使用递归
*
* @param head
* @return
*/
public Node reverseByRecursion (Node head, Node pre) {
if (head == null) {
return head;
}
if (head.next == null) {
head.next = pre;
return head;
}
Node next = head.next;
head.next = pre;
pre = head;
return reverseByRecursion(next, pre);
}
private static class Node {
int value;
Node next;
@Override
public String toString() {
return "Node{" +
"value=" + value +
", next=" + (next == null ? "" : next.value) +
'}';
}
}
private static void print (Node node) {
while (node != null) {
System.out.println(node);
node = node.next;
}
System.out.println();
}
public Node createList (int[] arr) {
if (arr.length == 0) {
return null;
}
Node head = new Node();
head.value = arr[0];
Node pointer = head;
for (int i = 1; i < arr.length; i++) {
Node node = new Node();
node.value = arr[i];
pointer.next = node;
pointer = pointer.next;
}
return head;
}
public static void main(String[] args) {
ReverseLinkedList reverseLinkedList = new ReverseLinkedList();
print(reverseLinkedList.reverseByIterative(reverseLinkedList.createList(new int[]{1,2,3,4})));
print(reverseLinkedList.reverseByIterative(reverseLinkedList.createList(new int[]{})));
print(reverseLinkedList.reverseByRecursion(reverseLinkedList.createList(new int[]{1,2,3,4}), null));
print(reverseLinkedList.reverseByRecursion(reverseLinkedList.createList(new int[]{}), null));
}
}
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