leetcode - Merge k Sorted Lists

문제

You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.

Merge all the linked-lists into one sorted linked-list and return it.

 

Example 1:

Input: lists = [[1,4,5],[1,3,4],[2,6]] Output: [1,1,2,3,4,4,5,6] Explanation: The linked-lists are: [ 1->4->5, 1->3->4, 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6

Example 2:

Input: lists = [] Output: []

Example 3:

Input: lists = [[]] Output: []

 

Constraints:

• k == lists.length
• 0 <= k <= 10^4
• 0 <= lists[i].length <= 500
• -10^4 <= lists[i][j] <= 10^4
• lists[i] is sorted in ascending order.
• The sum of lists[i].length won't exceed 10^4.

---

풀이

const mergeKLists = function (lists) {
    const merge = (l1, l2) => {
        if (!l1 || !l2) return l1 || l2;
        const node = ListNode(0);
        const root = node;
        while (l1 && l2) {
            if (l1.val <= l2.val) {
                node.next = l1;
                node = node.next;
                l1 = l1.next;
            } else {
                node.next = l2;
                node = node.next;
                l2 = l2.next;
            }
        }
        if (l1) node.next = l1;
        if (l2) nodex.next = l2;
        return root.next;
    };
    let root = lists[0];
    for (let i = 1; i < lists.length; i++) {
        root = merge(root, lists[i]);
    }
    return root || null;
};