【LeetCode】 23. Merge k Sorted Lists C語言

LeetCode解題心得，歡迎指正！

原題：合併k個排序的鏈接列表並將其作爲一個排序列表返回。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* mergeKLists(struct ListNode** lists, int listsSize) {
    
    return merge(lists,0,listsSize-1);
    
}

struct ListNode* merge(struct ListNode **lists, int begin ,int end)
{
    if(begin > end) return NULL;
    if(begin == end) return lists[begin];
    
    int mid=(begin+end)/2;
    struct ListNode *left=merge(lists,begin,mid);
    struct ListNode *right=merge(lists,mid+1,end);
    
    return merge_two_lists(left,right);
}

struct ListNode* merge_two_lists(struct ListNode *list1,struct ListNode *list2)
 {
     if(list1 == NULL) return list2;
     if(list2 == NULL) return list1;
     if(list1==NULL && list2==NULL) return NULL;
     struct ListNode *head=(struct ListNode *)malloc(sizeof(struct ListNode));
     struct ListNode *cur=head;
     
     while(list1 &&list2)
     {
         if(list1->val > list2->val)
         {
             cur->next=list2;
             list2=list2->next;
         }
         else
         {
             cur->next=list1;
             list1=list1->next;
         }
         cur=cur->next;
     }
     if(list1) cur->next=list1;
     if(list2) cur->next=list2;
     cur=head->next;
     free(head);
     return cur;
 }