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mergeKLists.cpp
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mergeKLists.cpp
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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
// 合并k个有序链表 思路:归并算法依次两两合并,
//时间复杂度O(nlogk) n是所有链表节点数 k是数组内链表个数 每次都几乎遍历了所有的结点 遍历了logK次
//空间复杂度O(1)
class Solution {
public:
ListNode* mergeKLists(vector<ListNode*>& lists) {
if (lists.size() == 0) return NULL;
return merge(lists, 0, lists.size()-1);
}
ListNode *merge(vector<ListNode *>& lists, int left, int right) {
if (left >= right) return lists[right];
int middle = left + (right-left)/2;
ListNode *l = merge(lists, left, middle);
ListNode *r = merge(lists, middle+1, right);
return mergeTwoList(l, r);
}
ListNode *mergeTwoList(ListNode *l1, ListNode *l2) {
if (l1 == NULL) return l2;
if (l2 == NULL) return l1;
ListNode *dummy = new ListNode(0);
ListNode *temp = dummy;
while(l1 && l2) {
if (l1->val < l2->val) {
temp->next = l1;
l1 = l1->next;
} else {
temp->next = l2;
l2 = l2->next;
}
temp = temp->next;
}
temp->next = l1 == NULL ? l2 : l1;
return dummy->next;
}
};