1669 Merge in Between Linked Lists - Leetcode

Approach

• Find the node at index a - 1 and b
• Set the next of the node at index
• Find the last node of list2
• Set the next of the last node of list2 to the next of the node at index b
• Return the head of the list

Complexity

Time complexity: O(n)

Space complexity: O(1)

Java Code

class Solution {
    public ListNode mergeInBetween(ListNode list1, int a, int b, ListNode list2) {
        ListNode start = list1;
        ListNode end = list1;
        for (int i = 0; i < a - 1; i++) {
            start = start.next;
        }
        for (int i = 0; i < b; i++) {
            end = end.next;
        }
        start.next = list2;
        while (list2.next != null) {
            list2 = list2.next;
        }
        list2.next = end.next;
        return list1; 
    }
}