Leetcode 线性表 Merge k Sorted Lists

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Merge k Sorted Lists

 Total Accepted: 10360 Total
Submissions: 44166

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

题意：将k个已排好序的链接合并成一个有序链表

思路：

利用Merge Two Sorted Lists的代码

两条两条地合并链表

复杂度：时间O(k*n)， 空间O(1)

/**
* 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) {
if(lists.empty()) return NULL;
ListNode *l1 = lists.front();
for(int i = 1; i < lists.size(); i++){
l1 = mergeTwoLists(l1, lists[i]);
}
return l1;
}

private:
ListNode *mergeTwoLists(ListNode *l1, ListNode *l2){
if(!l1) return l2;
if(!l2) return l1;
ListNode *l3, *cur;
ListNode dummy(-1);
l3 = cur = &dummy;
while(l1&&l2){
if(l1->val < l2->val) {
cur->next = l1;
l1 = l1->next;
}else{
cur->next = l2;
l2 = l2->next;
}
cur = cur->next;
}
if(l1) cur->next = l1;
else cur->next = l2;
return l3->next;

}

};