Leecode no.23 合并K个升序链表

package com.example.demo.leecode;

/**
 * 合并K个升序链表
 * @Date 2020/12/15
 * @author Tang
 *
 *  给你一个链表数组，每个链表都已经按升序排列。
 * 请你将所有链表合并到一个升序链表中，返回合并后的链表。
 */
public class MergeKSortedLists {

    public ListNode execute(ListNode[] lists){
        if(lists.length == 0){
            return null;
        }
        ListNode firstNode = lists[0];

        for(int i = 1; i < lists.length; i++){
            firstNode = mergeTwoList(firstNode, lists[i]);
        }

        return firstNode;
    }

    private ListNode mergeTwoList(ListNode l1, ListNode l2){
        ListNode first;
        ListNode end;
        if(l1.val <= l2.val){
            first = l1;
            l1 = l1.next;
        }else{
            first = l2;
            l2 = l2.next;
        }

        end = first;

        //循环排序成一条链表 直到其中一条到头了
        while(l1 != null && l2 != null){
            if(l1.val <= l2.val){
                end.next = l1;
                end = l1;
                l1 = l1.next;
            }else{
                end.next = l2;
                end = l2;
                l2 = l2.next;
            }

        }

        while(l1 != null){
            end.next = l1;
            end = l1;
            l1 = l1.next;
        }

        while(l2 != null){
            end.next = l2;
            end = l2;
            l2 = l2.next;
        }

        return first;
    }

    public static void main(String[] args) {

        ListNode l1 = new ListNode(1);
        ListNode l2 = new ListNode(2);
        ListNode l3 = new ListNode(3);
        ListNode l4 = new ListNode(5);

        ListNode l5 = new ListNode(2);
        ListNode l6 = new ListNode(4);
        ListNode l7 = new ListNode(8);
        ListNode l8 = new ListNode(9);

        ListNode l9 = new ListNode(2);
        ListNode l10 = new ListNode(3);
        ListNode l11 = new ListNode(4);
        ListNode l12 = new ListNode(5);

        l1.next = l2; l2.next = l3; l3.next = l4;
        l5.next = l6; l6.next = l7; l7.next = l8;
        l9.next = l10; l10.next = l11; l11.next = l12;

        ListNode[] list = {l1, l5, l9};
        ListNode execute = new MergeKSortedLists().execute(list);

        System.out.println(execute.val);
        while(execute.hasNext()){
            execute = execute.next;
            System.out.println(execute.val);

        }

    }
}

class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) {
        this.val = val;
    }
    ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }
    boolean hasNext(){
        return next != null;
    }

}