Merge Two Sorted Lists

LeetCode 21. Merge Two Sorted Lists 教學與筆記。

說明

Input: list1 = [1,2,4], list2 = [1,3,4]
Output: [1,1,2,3,4,4]

struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2){

    if(list1 == NULL){
        return list2;
    }
    if(list2 == NULL){
        return list1;
    }

    struct ListNode* dummy = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode* tail = dummy;

    while(list1 != NULL && list2 != NULL){
        if(list1->val <= list2->val){
            tail -> next = list1;
            list1 = list1 -> next;
        }
        else{
            tail -> next = list2;
            list2 = list2 -> next;
        }
        tail = tail -> next; // Move to either old list1 node or old list2 node
    }

    if(list1 == NULL){
        tail -> next = list2;
    }

    if(list2 == NULL){
        tail -> next = list1;
    }

    return dummy->next;
}

參考

LeetCode Merge Two Sorted Lists webpage
geeksforgeeks merge-two-sorted-linked-lists