Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
合并K个已拍好序的链表。剑指上有合并两个已排好序的链表的算法,那么K个数,我们可以采用归并排序的思想,不过合并函数可能需要修改一下,换成合并两个已排好序的链表的方法。代码如下:
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */
class Solution {
public:
ListNode* mergeKLists(vector<ListNode*>& lists) {
int len = lists.size();
if(len == 0) return NULL;
if(len == 1) return lists[0];
ListNode* ret = merge(lists,0,lists.size()-1);
return ret;
}
ListNode* merge(vector<ListNode*>& lists , int i,int j){
if(i==j) return lists[i];
ListNode* ret = NULL;
if(i<j){
int mid = (i+j)/2;
ListNode* lhs = merge(lists , i,mid);
ListNode* rhs = merge(lists , mid+1,j);
ret = mergeTwoLists(lhs,rhs);
}
return ret;
}
ListNode* mergeTwoLists(ListNode* list1 , ListNode* list2){
if(list1 == NULL) return list2;
if(list2 == NULL) return list1;
ListNode* ret = NULL;
if(list1->val < list2->val){
ret = list1;
ret->next = mergeTwoLists(list1->next , list2);
}
else{
ret = list2;
ret->next = mergeTwoLists(list1 , list2->next);
}
return ret;
}
};