Skip to main content

Function to sort an array using insertion sort

Insertion sort is slightly better sorting method among O(n2) algorithms. It is effecient if the elements are almost sorted and if the size is small.

Insertion sort basically works by splitting your elements into two parts. Sorted half and unsorted half. To begin with, Sorted half is empty and unsorted half has all elements. Then one element is removed from unsorted half and added to the sorted half. When adding , this element is inserted at the correct location. This process is continued till we have all the elements in sorted half and unsorted half is empty. Now let us try to understand it with a diagram.
First 17 is removed from unsorted array and added to sorted array. Since there is one element there, it is sorted. Next 4 which is front most element now in unsored array is removed and added to sorted array. But 4 is smaller than 17, so 17 is pushed to right and its place is taken by 4.
   Next 32 is removed from the front of unsorted array and added to sorted array. But here in sorted array to last element 17 is smaller. So 32 is in its correct place. Next 1 is moved from front of unsorted array. In sorted array, 32 is larger and pushed to right. Next 17 is pushed to right and 4 is also pushed to right. Now 1 is placed in 4's position. As you can see, now these 4 elements are sorted. This process continues until all the elements are removed from unsorted array.
   Removing front most element from the array takes O(1) X N elements. And inserting an element takes in worst case O(N) time. Hence complexity is O(N2 ) .
C++ function to insertion sort an array is really very simple and small.

#include<iostream>
using std::cin;
using std::cout;

void insertionSort(int *arr,int size);
void printArray(int *arr,int size);
int main()
{
    int n;
    cout<<"Size of array:";
    cin>>n;
    int a[n];
    cout<<"Elements of array:";
    for(int i=0;i<size;i++)
         cin>>a[i];
     insertionSort(a,n);
     printArray(a,n);
     return 0;
}

void insertionSort(int *arr,int size)
{
   for(int i=1;i<size;i++)
   {
        int val = arr[i];
        int j;
        for(j=i-1;j>=0 && arr[j] >val;j--)
        {
                 arr[j+1]=arr[j];
         }
         arr[j+1]=val;
   }
}


void printArray(int *arr,int size)
{
     for(int i=0;i<size;i++) 
            cout<< arr[i]<<"=====";
 
 }

In the insertionSort function, outer loop is for extracting one element from unsorted array. And inner loop is for inserting it in the sorted array and pushing elements to right as needed.
Writing insertion sort for linked list is much simple as well. You take one more linked list - sortedList. Now remove front element from list and insert it in ascending order in sortedList.
Labels:

Comments

Post a Comment

Popular posts from this blog

Linked list in C++

A linked list is a versatile data structure. In this structure, values are linked to one another with the help of addresses. I have written in an earlier post about how to create a linked list in C.  C++ has a library - standard template library which has list, stack, queue etc. data structures. But if you were to implement these data structures yourself in C++, how will you implement? If you just use new, delete, cout and cin, and then claim it is your c++ program, you are not conforming to OOPS concept. Remember you have to "keep it together". Keep all the functions and variables together - in a class. You have to have class called linked list in which there are methods - append, delete, display, insert, find, find_last. And there will also be a data - head. Defining node We need a structure for all these nodes. A struct can be used for this purpose, just like C. struct node { int val; struct node * next; }; Next we need to define our class. W
Post a Comment
Read more

Swap nodes of a linked list

Qn: Write a function to swap the adjacent nodes of a singly linked list.i.e. If the list has nodes as 1,2,3,4,5,6,7,8, after swapping, the list should be 2,1,4,3,6,5,8,7 Image from: https://tekmarathon.com Though the question looks simple enough, it is tricky because you don't just swap the pointers. You need to take care of links as well. So let us try to understand how to go about it. Take two adjacent nodes p1 and p2 Let prevnode be previous node of p1 Now link prevnode to p2 Link p2 to p1 Link p1 to next node of p2 So the code will be prevnode -> next = p2; p1 -> next = p2 -> next; p2 -> next = p1; But what about the start node or head? head node does not have previous node If we swap head with second node, modified head should be sent back to caller  To take care of swapping first and second nodes, we can write p1 = head; p2 = head -> next; p1 -> next = p2 -> next; p2 -> next = p1; head = p2;  Now we are read
Post a Comment
Read more

Binary tree deletion - non-recursive

In the previous post we have seen how to delete a node of a binary search tree using recursion. Today we will see how to delete a node of BST using a non-recursive function. Let us revisit the 3 scenarios here Deleting a node with no children just link the parent to NULL Deleting a node with one child link the parent to  non-null child of node to be deleted Deleting a node with both children select the successor of node to be deleted copy successor's value into this node delete the successor In order to start, we need a function to search for a node in binary search tree. Did you know that searching in  a BST is very fast, and is of the order O(logn). To search Start with root Repeat until value is found or node is NULL If the search value is greater than node branch to right If the search value is lesser than node branch to left.  Here is the function NODEPTR find_node (NODEPTR root,NODEPTR * parent, int delval) { NODEPTR nd = root; NODEPTR pa = root; if (root -> v
Post a Comment
Read more