1669.MergeInBetween.cs

// 1669. Merge In Between Linked Lists
// You are given two linked lists: list1 and list2 of sizes n and m respectively.
// Remove list1's nodes from the ath node to the bth node, and put list2 in their place.
// The blue edges and nodes in the following figure indicate the result:
// Build the result list and return its head.
// Example 1:
// Input: list1 = [10,1,13,6,9,5], a = 3, b = 4, list2 = [1000000,1000001,1000002]
// Output: [10,1,13,1000000,1000001,1000002,5]
// Explanation: We remove the nodes 3 and 4 and put the entire list2 in their place. The blue edges and nodes in the above figure indicate the result.
// Example 2:
// Input: list1 = [0,1,2,3,4,5,6], a = 2, b = 5, list2 = [1000000,1000001,1000002,1000003,1000004]
// Output: [0,1,1000000,1000001,1000002,1000003,1000004,6]
// Explanation: The blue edges and nodes in the above figure indicate the result.

// Constraints:
// 3 <= list1.length <= 104
// 1 <= a <= b < list1.length - 1
// 1 <= list2.length <= 104

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode MergeInBetween(ListNode list1, int a, int b, ListNode list2) {
        int i = 0;
        ListNode Start, Curr, End;
        Start = Curr = list1;
        //iterate to the ath node
        while(i < a-1){
            Curr = Curr.next; 
            i++;
        }
        //save the ath node as Start of the list to be removed
        Start = Curr;
        //iterate to the bth node to save it as End of the list to be removed
        while(i <= b){
            Curr = Curr.next;
            i++;
        }
        //save the bth node as End of the list to be removed
        End = Curr;
        //connect the list1 to list2
        Start.next = list2;
        //iterate to the end of list2
        while(Start.next != null){
            Start = Start.next;
        }
        //connect the end of list2 to the list1
        Start.next = End;
        return list1;
    }
}