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merge sort linked list java

Ayan Ghazi answered on July 26, 2022 Popularity 9/10 Helpfulness 6/10

answer merge sort linked list java

merge sort linked list java

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode sortList(ListNode head) {
        if(head == null || head.next == null)
            return head;
        
        ListNode slow = head;
        ListNode fast = head;
        ListNode prev = head;
        while(fast != null && fast.next != null){
            prev = slow;
            slow =slow.next;
            fast = fast.next.next;
        }
        
        prev.next = null;
        
        ListNode mid = slow;
        
        ListNode left = sortList(head);
        ListNode right = sortList(mid);
        
        return merge(left, right);
    }
    
    public ListNode merge(ListNode list1, ListNode list2) {
        
        ListNode l = new ListNode(0), p = l;
    
    while (l1 != null && l2 != null) {
      if (l1.val < l2.val) {
        p.next = l1;
        l1 = l1.next;
      } else {
        p.next = l2;
        l2 = l2.next;
      }
      p = p.next;
    }
    
    if (l1 != null)
      p.next = l1;
    
    if (l2 != null)
      p.next = l2;
    
    return l.next;
  }
}

Popularity 9/10 Helpfulness 6/10 Language java

Source: Grepper

Tags: java linked-list merge

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Contributed on Jul 26 2022

Ayan Ghazi

0 Answers Avg Quality 2/10

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merge sort and linked list

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def merge_sort(linked_list):
    """
    Sorts a linked list in ascending order
    - Recursively divide the linked list into sublists containing a single node
    - Repeatedly merge the sublists to produce sorted sublists until one remains

    Returns a sorted linked list

    Takes O(n log n) time
    Takes O(n) space
    """
    if linked_list.size() == 1:
        return linked_list
    elif linked_list.head is None:
        return linked_list

    left_half, right_half = split(linked_list)
    left = merge_sort(left_half)
    right = merge_sort(right_half)

    return merge(left, right)

def split(linked_list):
    """
    Divide the unsorted list at midpoint into sublists
    Takes O(log n) time
    """
    if linked_list == None or linked_list.head == None:
        left_half = linked_list
        right_half = None

        return left_half, right_half
    else:
        size = linked_list.size()
        mid = size//2
        mid_node = linked_list.node_at_index(mid-1)

        left_half = linked_list
        right_half = LinkedList()
        right_half.head = mid_node.next_node
        mid_node.next_node = None

        return left_half, right_half


def merge(left, right):
    """
    Merges two linked lists, sorting by data in nodes
    Returns a new merged list
    Takes O(n) space
    Runs in O(n) time
    """

    # Create a new linked list that contains nodes from merging left and right
    merged = LinkedList()
    # Add a fake head that is discarded later.
    merged.add(0)
    # Set current to the head of the linked list
    current = merged.head

    # Obtain head nodes for left and right linked lists
    left_head = left.head
    right_head = right.head

    # Iterate over left and right as long until the tail node of both
    # left and right
    while left_head or right_head:
        # If the head node of left is None, we're at the tail
        # Add the tail node from right to the merged linked list
        if left_head is None:
            current.next_node = right_head
            # Call next on right to set loop condition to False
            right_head = right_head.next_node 
        # If the head node of right is None, we're at the tail
        # Add the tail node from left to the merged linked list
        elif right_head is None:
            current.next_node = left_head
            # Call next on left to set loop condition to False
            left_head = left_head.next_node
        else:
            # Not at either tail node
            # Obtain node data to perform comparison operations
            left_data = left_head.data
            right_data = right_head.data

            # If data on left is lesser than right set current to left node
            # Move left head to next node
            if left_data < right_data:
                current.next_node = left_head
                left_head = left_head.next_node
            # If data on left is greater than right set current to right node
            # Move right head to next node
            else:
                current.next_node = right_head
                right_head = right_head.next_node

        # Move current to next node
        current = current.next_node

    # Discard fake head and set first merged node as head
    head = merged.head.next_node
    merged.head = head

    return merged

Popularity 8/10 Helpfulness 1/10 Language whatever

Source: teamtreehouse.com

Tags: linked-list link

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Contributed on Dec 26 2023

Chow Banana

0 Answers Avg Quality 2/10

merge sort linked list java

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