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merge sort and linked list

Chow Banana answered on February 24, 2022 Popularity 7/10 Helpfulness 1/10

answer merge sort and linked list

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 7/10 Helpfulness 1/10 Language whatever

Source: teamtreehouse.com

Tags: linked-list merge whatever

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Contributed on Dec 26 2023

Chow Banana

0 Answers Avg Quality 2/10

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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 linke

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Contributed on Jul 26 2022

Ayan Ghazi

0 Answers Avg Quality 2/10

linked list in merge sort python

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# Python3 program to merge sort of linked list
 
# create Node using class Node.
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
class LinkedList:
    def __init__(self):
        self.head = None
     
    # push new value to linked list
    # using append method
    def append(self, new_value):
         
        # Allocate new node
        new_node = Node(new_value)
         
        # if head is None, initialize it to new node
        if self.head is None:
            self.head = new_node
            return
        curr_node = self.head
        while curr_node.next is not None:
            curr_node = curr_node.next
             
        # Append the new node at the end
        # of the linked list
        curr_node.next = new_node
         
    def sortedMerge(self, a, b):
        result = None
         
        # Base cases
        if a == None:
            return b
        if b == None:
            return a
             
        # pick either a or b and recur..
        if a.data <= b.data:
            result = a
            result.next = self.sortedMerge(a.next, b)
        else:
            result = b
            result.next = self.sortedMerge(a, b.next)
        return result
     
    def mergeSort(self, h):
         
        # Base case if head is None
        if h == None or h.next == None:
            return h
 
        # get the middle of the list
        middle = self.getMiddle(h)
        nexttomiddle = middle.next
 
        # set the next of middle node to None
        middle.next = None
 
        # Apply mergeSort on left list
        left = self.mergeSort(h)
         
        # Apply mergeSort on right list
        right = self.mergeSort(nexttomiddle)
 
        # Merge the left and right lists
        sortedlist = self.sortedMerge(left, right)
        return sortedlist
     
    # Utility function to get the middle
    # of the linked list
    def getMiddle(self, head):
        if (head == None):
            return head
 
        slow = head
        fast = head
 
        while (fast.next != None and
               fast.next.next != None):
            slow = slow.next
            fast = fast.next.next
             
        return slow
         
# Utility function to print the linked list
def printList(head):
    if head is None:
        print(' ')
        return
    curr_node = head
    while curr_node:
        print(curr_node.data, end = " ")
        curr_node = curr_node.next
    print(' ')
     
# Driver Code
if __name__ == '__main__':
    li = LinkedList()
     
    # Let us create a unsorted linked list
    # to test the functions created.
    # The list shall be a: 2->3->20->5->10->15
    li.append(15)
    li.append(10)
    li.append(5)
    li.append(20)
    li.append(3)
    li.append(2)
     
    # Apply merge Sort
    li.head = li.mergeSort(li.head)
    print ("Sorted Linked List is:")
    printList(li.head)
 
# This code is contributed by Vikas Chitturi

Popularity 9/10 Helpfulness 2/10 Language python

Source: www.geeksforgeeks.org

Tags: linked-list link

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Contributed on Feb 24 2022

Green Team

0 Answers Avg Quality 2/10

merge two sorted linked list

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class ListNode {
    val: number
    next: ListNode | null
    constructor(val?: number, next?: ListNode | null) {
        this.val = (val === undefined ? 0 : val)
        this.next = (next === undefined ? null : next)
    }
}

function mergeTwoLists(list1: ListNode | null, list2: ListNode | null): ListNode | null {
    if (!list1) return list2
    if (!list2) return list1
    if (!list1 && !list2) return null

    let sorted = new ListNode(), current = sorted

    while (list1 && list2) {
        if (list1.val < list2.val) {
            current.next = list1;
            list1 = list1.next
        } else {
            current.next = list2
            list2 = list2.next
        }
        current = current.next
    }

    current.next = list1 || list2
    return sorted.next
};

Popularity 8/10 Helpfulness 2/10 Language typescript

Source: chat.openai.com

Tags: linked-list link

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Contributed on Dec 05 2023

Samuel Izevbizua

0 Answers Avg Quality 2/10

Linked Lists - Sorted Merge

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function Node(data) {
  this.data = data === undefined ? null : data;
  this.next = null;
}

function sortedMerge(first, second) {
  
 let a = new Node()
 const dummy = a
  
  
  while(first  && second ){
    if( first.data <second.data){
      a.next = first
      first = first.next
    }
    else{
      a.next= second
      second= second.next
    }
    a= a.next
    }
    
 
    if(first){
      a.next=first
    }
    if(second){
      a.next = second
    }
 
  
     return dummy.next
  
  
}

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: Grepper

Tags: javascript j

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Contributed on Jul 16 2022

ABS

0 Answers Avg Quality 2/10

merge sort and linked list

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