mergeKList

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     public int val;
 *     public ListNode next;
 *     ListNode(int x) { val = x; next = null; }
 * }
 */
public class Solution {

	public ListNode mergeKLists(ArrayList<ListNode> A) {

	    TreeMap<Integer, ArrayList<ListNode>> map = new TreeMap<>();
	    ListNode node;
	    ArrayList<ListNode> list;
	    int val;

	    for (ListNode head : A) {
	        node = head;
	        while (node != null) {
	            val = node.val;

	            if (map.containsKey(val)) {
	                list = map.get(val);
	                list.add(node);
	            } else {
	                list = new ArrayList<>();
	                list.add(node);
	                map.put(val, list);
	            }

	            node = node.next;
	        }
	    }

	    ListNode head = null;
	    node = null;

	    for (Map.Entry<Integer, ArrayList<ListNode>> entry : map.entrySet()) {

	        list = entry.getValue();

	        for (ListNode n : list) {
	            if (head == null)
	                head = n;
	            if (node != null)
	                node.next = n;
	            node = n;
	        }


	    }

	    return head;

	}