java 23.合并k个排序列表（＃）。java

Posted 2021-05-08

//This is a classic interview question. Another similar problem is "merge k sorted lists".

//This problem can be solved by using a heap. The time is O(nlog(n)).

//Given m arrays, the minimum elements of all arrays can form a heap. It takes O(log(m)) to insert an element to the heap and it takes O(1) to delete the minimum element.

class ArrayContainer implements Comparable<ArrayContainer> {
	int[] arr;
	int index;
 
	public ArrayContainer(int[] arr, int index) {
		this.arr = arr;
		this.index = index;
	}
 
	@Override
	public int compareTo(ArrayContainer o) {
		return this.arr[this.index] - o.arr[o.index];
	}
}
public class KSortedArray {
	public static int[] mergeKSortedArray(int[][] arr) {
		//PriorityQueue is heap in Java 
		PriorityQueue<ArrayContainer> queue = new PriorityQueue<ArrayContainer>();
		int total=0;
 
		//add arrays to heap
		for (int i = 0; i < arr.length; i++) {
			queue.add(new ArrayContainer(arr[i], 0));
			total = total + arr[i].length;
		}
 
		int m=0;
		int result[] = new int[total];
 
		//while heap is not empty
		while(!queue.isEmpty()){
			ArrayContainer ac = queue.poll();
			result[m++]=ac.arr[ac.index];
 
			if(ac.index < ac.arr.length-1){
				queue.add(new ArrayContainer(ac.arr, ac.index+1));
			}
		}
 
		return result;
	}
 
	public static void main(String[] args) {
		int[] arr1 = { 1, 3, 5, 7 };
		int[] arr2 = { 2, 4, 6, 8 };
		int[] arr3 = { 0, 9, 10, 11 };
 
		int[] result = mergeKSortedArray(new int[][] { arr1, arr2, arr3 });
		System.out.println(Arrays.toString(result));
	}
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        if(lists.length == 0)
            return null;
        return partition(0, lists.length - 1, lists);
    }
    
    public ListNode partition(int i, int j, ListNode[] lists){
        if(i == j)
            return lists[i];
        ListNode l1 = partition(i, (i + j) / 2, lists);
        ListNode l2 = partition((i + j) / 2 + 1, j, lists);
        return merge(l1, l2);
    }
    
    public ListNode merge(ListNode l1, ListNode l2){
        if(l1 == null) 
            return l2;
        if(l2 == null)
            return l1;
        ListNode head = null;
        if(l1.val < l2.val){
            head = l1;
            head.next = merge(l1.next, l2);
        }else{
            head = l2;
            head.next = merge(l1, l2.next);
        }
        return head;
    }
    
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        if (lists.length==0) return null;
        int start = 0;
        int end = lists.length-1;
        while(end>0){
            start=0;
        while(start<end){
            lists[start]=merge2(lists[start],lists[end]);
            start++;
            end--;
        } }
        return lists[0];
    }
    private ListNode merge2(ListNode l1,ListNode l2){
        ListNode newh = new ListNode(1);
        ListNode p= newh;
        ListNode p1=l1;
        ListNode p2=l2;
        while(p1!=null&&p2!=null){
            if(p1.val<=p2.val){
                p.next=p1;
                p1=p1.next;
                p=p.next;
            }
            else{
                p.next=p2;
                p2=p2.next;
                p=p.next;
            }
        }
        if(p1!=null){
            p.next=p1;
        }
        if(p2!=null){
            p.next=p2;
        }
        return newh.next;
    }
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
         int len = lists.length;
        if (len == 0) {
            return null;
        }
//        ListNode listNode = lists[0];
//        for (int i = 1; i < len; i++) {
//            if (lists[i] == null)
//                continue;
//            if (listNode == null) {
//                listNode = lists[i];
//                continue;
//            }
//            listNode = mergeTwoKLists(listNode, lists[i]);
//        }
        return  mergeKLists(lists,0,len-1);
    }
    public static ListNode mergeKLists(ListNode[] lists, int l, int r) {
        if (l > r)
            return null;
        if (r == l)
            return lists[r];
        if (r - l == 1) {
            return mergeTwoKLists(lists[l], lists[r]);
        }
        int mid = (l + r) >> 1;
        ListNode lNode = mergeKLists(lists, l, mid);
        ListNode rNode = mergeKLists(lists, mid + 1, r);
        return mergeTwoKLists(lNode, rNode);
    }

     public static ListNode mergeTwoKLists(ListNode left  ,ListNode right) {
        if (right == null)
            return left;
        if (left==null)
            return  right;
        ListNode tmp,root;
        if (left.val>=right.val){
            tmp=right;
            right=right.next;
        }
        else {
            tmp=left;
            left=left.next;
        }
        root=tmp;
        while (left!=null&&right!=null){
            if (left.val>right.val){
                tmp.next=right;
                right=right.next;
                tmp=tmp.next;
            }
            else {
                tmp.next=left;
                left=left.next;
                tmp=tmp.next;
            }
        }
        if (left!=null)
            tmp.next=left;
        if (right!=null)
            tmp.next=right;

        return root;
    }
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
    
        if( lists == null || lists.length == 0) return null;
        
        PriorityQueue<ListNode> q = new PriorityQueue<ListNode>(new Comparator<ListNode>(){
            public int compare(ListNode n1, ListNode n2){
                return n1.val - n2.val;
            }
        });
        
        for(ListNode list:lists){
            if(list != null)
                q.offer(list);
        }
        
        ListNode head = new ListNode(-1);
        ListNode temp = head;
        
        while(!q.isEmpty()){
            ListNode n = q.poll();
            temp.next = n;
            temp = temp.next;
            
            if(n.next != null)
                q.offer(n.next);
        }
        
        return head.next;
        
    }
}