LeetCode:Merge k Sorted Lists

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思路：归并排序

/**
 * 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.size() == 0) return NULL;
        return mergeSort(lists,0,lists.size()-1);
    }
    
    ListNode *mergeSort(vector<ListNode*>& lists, int s, int e){
        if(s==e) return lists[s];
        else {
            int mid = (s+e)>>1;
            ListNode *l1 = mergeSort(lists,s,mid);
            ListNode *l2 = mergeSort(lists,mid+1,e);
            return merge(l1,l2);
        }
    }
    ListNode *merge(ListNode *l1, ListNode *l2){
        if(l1==NULL) return l2;
        if(l2==NULL) return l1;
        ListNode dummy(0);
        ListNode *p = &dummy;
        while(l1 && l2){
            if(l1->val < l2->val){
                p->next = l1;
                l1=l1->next;
            }
            else {
                p->next = l2;
                l2=l2->next;
            }
            p = p->next;
        }
        p->next = l1!=NULL?l1:l2;
        return dummy.next;
    }
    
};

LeetCode:Merge k Sorted Lists

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原文地址：http://blog.csdn.net/itismelzp/article/details/51167618