合并两个链表

/* 
 * Problem: Similar to the Java solution, but using Java Streams for practice. 
 * 
 * Note: Java Streams are generally used for collections, not linked lists. 
 * This solution is a conceptual use of Streams and may not be optimal for linked lists. 
 */ 

import java.util.stream.*; 
import java.util.*; 

class ListNode { 
    int val; 
    ListNode next; 
    ListNode(int val) { this.val = val; } 
}

public class StreamSolution { 
    public ListNode mergeInBetween(ListNode list1, int a, int b, ListNode list2) { 
        List<ListNode> listNodes = new ArrayList<>(); 

        // Convert list1 to a stream and collect nodes into a list
        ListNode current = list1; 
        while (current != null) { 
            listNodes.add(current); 
            current = current.next; 
        } 

        // Find preA and postB using indexes a and b
        ListNode preA = listNodes.get(a - 1); 
        ListNode postB = listNodes.get(b + 1); 

        // Connect preA to list2's head
        preA.next = list2; 

        // Find the tail of list2
        ListNode tail2 = list2; 
        while (tail2.next != null) { 
            tail2 = tail2.next; 
        } 

        // Connect the tail of list2 to postB
        tail2.next = postB; 

        return list1; 
    } 
}