mergek.java

//https://leetcode.com/problems/merge-k-sorted-lists

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
       if(lists.length == 0) return null;

        int interval = 1;
        int len = lists.length;
        while(interval<len){
            for(int i=0;i<len-interval;i+=(interval*2)){
                merge(lists,i,i+interval);
            }
            interval*=2;
        }
        return lists[0];
    }

    public void merge(ListNode[] lists,int in1,int in2){
        ListNode ans = new ListNode(-1);
        ListNode ptr = ans;
        ListNode l1 = lists[in1];
        ListNode l2 = lists[in2];

        while(l1!=null || l2!=null){
            if(l1==null){
                ptr.next = l2;
                break;
            }
            if(l2==null) {
                ptr.next = l1;
                break;
            }

            if(l1.val<l2.val){
                ptr.next = l1;
                l1 = l1.next;
            }
            else{
                ptr.next  = l2;
                l2 = l2.next;
            }
            ptr = ptr.next;
        }
        lists[in1] = ans.next;
    }
}