104题 Merge K Sorted Lists

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本文介绍了一种算法，用于合并多个已排序的链表成为一个单一的排序链表，并提供了详细的实现过程。通过两两合并的方式逐步将所有链表合并为一个链表。

Merge K Sorted Lists

Description
Merge k sorted linked lists and return it as one sorted list.

Analyze and describe its complexity.

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */ 
public class Solution {
    /**
     * @param lists: a list of ListNode
     * @return: The head of one sorted list.
     */
    public ListNode mergeKLists(List<ListNode> lists) {  
        // write your code here
        int size = lists.size() ;
        if(lists == null && lists.size() == 0){
            return null ;
        }
        ListNode head1 = lists.get(0) ;
        for(int i = 1 ; i < lists.size()  ; i++ ){
            ListNode head2 = lists.get(i) ;
            head1 = merge(head1 , head2) ;
        }
        return head1 ;

    }
    public ListNode merge(ListNode head1 , ListNode head2){
        ListNode dummy = new ListNode(0);
        ListNode tail = dummy ;
        while(head1 != null && head2 != null){
            if(head1.val < head2.val){
                tail.next = head1 ;
                head1 = head1.next ;
            }else{
                tail.next = head2 ;
                head2 = head2.next ;
            }
            tail = tail.next ;
        }
        if(head1 != null){
            tail.next = head1 ;
        }else{
            tail.next = head2 ;
        }
        return dummy.next ;
    }
}