leetcode | Merge Two Sorted Lists

Merge Two Sorted Lists

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.

C实现

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
 //时间复杂度O(min(m, n)) 空间复杂度O(1)
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
    if (l1 == NULL || l2 == NULL)
        return (l1 == NULL) ? l2 : l1;
    struct ListNode* dummy = (struct ListNode*)malloc(sizeof(*dummy));//假节点
    struct ListNode* prev = dummy;
    while (l1 && l2) {
        if (l1->val < l2->val) {
            prev->next = l1;
            l1 = l1->next;
        } else {
            prev->next = l2;
            l2 = l2->next;
        }
        prev = prev->next;
    }
    prev->next = (l1 == NULL) ? l2 : l1;
    return dummy->next;

}