题解 | #合并k个已排序的链表#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
#include <vector>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param lists ListNode类vector 
     * @return ListNode类
     */
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        // write code here
        vector<int> nums;
        for(int i=0;i<lists.size();i++){
            ListNode* p=lists[i];
            while(p!=nullptr){
                nums.push_back(p->val);
                p=p->next;
            }
        }
        return heapsort(nums, nums.size());
    }
private:
    ListNode* heapsort(vector<int> nums,int heapsize){
        ListNode* res=new ListNode(0);
        ListNode *p=res;
        for(int i=(heapsize-1)/2;i>=0;i--){
            heapify_down(nums, nums.size(),i);
        }
        for(int i=heapsize-1;i>=0;i--){
            ListNode* tmp=new ListNode(nums[0]);
            p->next=tmp;
            p=tmp;
            swap(nums[0],nums[i]);
            heapsize--;
            heapify_down(nums, heapsize, 0);
        }
        return res->next;
    }
    void heapify_down(vector<int> &nums,int heapsize,int i){//小根堆
        int largest=i;
        int left=2*i+1;
        int right=2*i+2;
        if(left<heapsize&&nums[largest]>nums[left]){
            largest=left;
        }
        if(right<heapsize&&nums[largest]>nums[right]){
            largest=right;
        }
        if(largest!=i){
            swap(nums[largest],nums[i]);
            heapify_down(nums,heapsize, largest);
        }
    }
};