java ķ个有序链表的归并

Posted 2021-05-08

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class MergeKLists {
    public ListNode mergeKLists(ListNode[] lists) {
        if(lists == null || lists.length == 0) {
            return null;
        }
        return merge(lists,0,lists.length-1);
    }
    
    private ListNode merge(ListNode[] lists, int low, int high) {
        if(low<high) {
            int mid = low+(high-low)/2;
            ListNode left = merge(lists,low,mid);
            ListNode right = merge(lists,mid+1,high);
            return mergeTwoLists(left, right);
        }
        return lists[low];
    }
    
    private ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode p = l1, q = l2;
        ListNode dummy = new ListNode(-1);
        ListNode r = dummy;
        while(p!=null || q!=null) {
            if(p == null) {
                r.next = q;
                break;
            } else if(q == null) {
                r.next = p;
                break;
            } else if(p.val < q.val) {
                r.next = p;
                p = p.next;
                r = r.next;
            } else {
                r.next = q;
                q = q.next;
                r = r.next;
            }
        }
        return dummy.next;
    }
}