反转链表

/*
 * Problem: Reverse a singly linked list using Java Stream API.
 * Approach: Java Streams are not typically used for linked list manipulation, but we can convert the list to a stack and then to a new list.
 */
 
import java.util.LinkedList;
import java.util.List;
import java.util.Stack;
 
class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}
 
public class Solution {
    public ListNode reverseList(ListNode head) {
        Stack<Integer> stack = new Stack<>();
        ListNode curr = head;
        while (curr != null) {
            stack.push(curr.val); // Push all elements to the stack
            curr = curr.next;
        }
        ListNode newHead = new ListNode(0); // Dummy head
        ListNode newCurr = newHead;
        while (!stack.isEmpty()) {
            newCurr.next = new ListNode(stack.pop()); // Pop from stack to new list
            newCurr = newCurr.next;
        }
        return newHead.next; // Return the new head
    }
}