【LeetCode】Merge Two Sorted Lists & Merge k Sorted Lists

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本文详细介绍了如何将两个已排序的链表合并为一个排序链表，并提供了复杂度分析。接着，深入探讨了合并k个已排序链表的技术，包括算法实现和性能考量。

Merge Two Sorted Lists

Total Accepted: 20769 Total Submissions: 62658 My Submissions

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Merge k Sorted Lists

Total Accepted: 15334 Total Submissions: 70273 My Submissions

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        if (l1 == NULL) return l2;
        if (l2 == NULL) return l1;
        ListNode *head = NULL;
        if (l1->val < l2->val) {
            head = l1;
            l1 = l1->next;
        } else {
            head = l2;
            l2 = l2->next;
        }
        head->next = NULL;
        ListNode *p = head;
        while (l1 && l2) {
            if (l1->val < l2->val) {
                p->next = l1;
                l1 = l1->next;
            } else {
                p->next = l2;
                l2 = l2->next;
            }
            p = p->next;
            p->next = NULL;
        }
        if (l1) {
            p->next = l1;
            return head;
        }
        if (l2) {
            p->next = l2;
            return head;
        }
    }
    ListNode *mergeKLists(vector<ListNode *> &lists) {
        ListNode *head = NULL;
        for(int i = 0; i < lists.size(); i++)
        {
            head = mergeTwoLists(head, lists[i]);
        }
        return head;
    }
};