Merge k Sorted Lists

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

第一遍：

public class Solution {
    public ListNode mergeKLists(ArrayList<ListNode> lists) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(lists.size()==0) return null;
        ListNode header = new ListNode(-1), cur = header;
        // boolean sig = true;
        while(true){
            int pos = -1;
            for(int i = 0; i < lists.size(); i ++){
                if(lists.get(i) != null && (pos == -1 || lists.get(i).val < lists.get(pos).val))
                    pos = i;
            }
            if(pos != -1){
                cur.next = lists.get(pos);
                cur = cur.next;
                lists.set(pos,lists.get(pos).next);

            }else{
                break;
            }
        }
        return header.next;
    }
}

第三遍：

去掉 null的项 可以加速 查找。

public class Solution {
    public ListNode mergeKLists(ArrayList<ListNode> lists) {
        ListNode header = new ListNode(-1);
        ListNode cur = header;
        if(lists == null || lists.size() == 0) return null;
        while(true){
            int min = -1;
            for(int i = 0; i < lists.size(); i ++){
                if(lists.get(i) == null){
                    lists.remove(i);
                    i --;
                }
                else if(min == -1 || lists.get(i).val < lists.get(min).val)
                    min = i;
            }
            if(min == -1) break;
            else{
                cur.next = lists.get(min);
                lists.set(min,lists.get(min).next);
                cur = cur.next;
            }
        }
        return header.next;
    }
}