[LeetCode]Merge Sorted Lists

参考  友链

public class Solution {
    
    public ListNode mergeKLists(ListNode[] lists) {
        if(lists == null || lists.length == 0 ){
            return null;
        }
        return mergeKLists(lists,0,lists.length-1);
    }
    
    public ListNode mergeKLists(ListNode[] lists, int left, int right){
        if(left < right){
            int mid = (left + right)/2;
            return merge(mergeKLists(lists,left,mid),mergeKLists(lists,mid+1,right));
        }
        return lists[left];
    }
    
    public ListNode merge(ListNode n1, ListNode n2){
        ListNode head =  new ListNode(0);
        ListNode n = head;
        while(n1 != null && n2 != null){
            if(n1.val < n2.val){
                n.next = n1;
                n1 = n1.next;
                n = n.next;
            }else{
                n.next = n2;
                n = n.next;
                n2 = n2.next;
            }
        }
        if( n1 != null){
            n.next = n1;
        }else{
            n.next = n2;
        }
        return head.next;
    }
 
}



public class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        if(lists == null || lists.length == 0){
            return null;
        }
        PriorityQueue
  
    queue = new PriorityQueue
   
    (lists.length,new Comparator
    
     (){
            @Override
            public int compare(ListNode n1, ListNode n2){
                return n1.val - n2.val;
            }
            });
            
        for(ListNode n : lists){
            if(n != null)
                queue.add(n);
        }
        ListNode head = new ListNode(0);
        ListNode n = head;
        while(!queue.isEmpty()){
            ListNode temp = queue.poll();
            n.next = temp;
            n = n.next;
            if(temp.next != null)
                queue.offer(temp.next);
        }
        return head.next;
    }
}