Merge k Sorted Lists 分类： Leetcode（树） 2015-04-09 09:35 17人阅读 评论(0) 收藏

Merge k Sorted Lists

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

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *merge2List(ListNode *h1, ListNode *h2) {
        ListNode dummy(-1);
        ListNode *tail = &dummy;
        while( h1 && h2) {
            if(h1->val > h2->val) {
                tail->next = h2;
                h2 = h2->next;
            } else {
                tail->next =h1;
                h1 = h1->next;
            }
            tail = tail->next;
        }
        
        if(h1) tail->next = h1;
        if(h2) tail->next = h2;
        return dummy.next;
    }

    ListNode *sort(int start, int len, vector<ListNode*> &lists) {
        if(!len) return nullptr;
        if(len == 1) return lists[start];
        ListNode *h1 = sort(start, len/2,lists);
        ListNode *h2 = sort(start+len/2, len -len/2,lists);
        return merge2List(h1,h2);
    }

    ListNode *mergeKLists(vector<ListNode *> &lists) {
        return sort(0, lists.size(),lists);
    }

};

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