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

Merge Two Sorted Lists

 Total Accepted: 20769 Total Submissions: 62658My 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: 70273My 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;    }};