1669. Merge In Between Linked Lists

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題目敘述

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.

// Definition for singly-linked list.
public class ListNode {
    int val;
    ListNode next;

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

解題思路

Solution

class Solution {
    public ListNode mergeInBetween(ListNode list1, int a, int b, ListNode list2) {
        ListNode head = new ListNode();
        head.next = list1;

        ListNode prev = head;
        for (int i = 0; i < a; i++) {
            prev = prev.next;
        }

        ListNode next = prev;
        for (int i = 0; i < b - a + 1; i++) {
            next = next.next;
        }

        prev.next = list2;
        while (list2.next != null) {
            list2 = list2.next;
        }

        list2.next = next.next;

        return head.next;
    }
}