Saturday, 30 April 2016

Insertion Sort in C++

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Insertion sort is a simple sorting algorithm that works the way we sort playing cards in our hands.


Insertion Sort

Insertion Sort

Algorithm
// Sort an arr[] of size n
insertionSort(arr, n)
Loop from i = 1 to n-1.
……a) Pick element arr[i] and insert it into sorted sequence arr[0…i-1]

Example:
12, 11, 13, 5, 6

Let us loop for i = 1 (second element of the array) to 5 (Size of input array)

i = 1. Since 11 is smaller than 12, move 12 and insert 11 before 12
11, 12, 13, 5, 6

i = 2. 13 will remain at its position as all elements in A[0..I-1] are smaller than 13
11, 12, 13, 5, 6

i = 3. 5 will move to the beginning and all other elements from 11 to 13 will move one position ahead of their current position.
5, 11, 12, 13, 6

i = 4. 6 will move to position after 5, and elements from 11 to 13 will move one position ahead of their current position.
5, 6, 11, 12, 13


Code:
// C program for insertion sort
#include<iostream>
#include<math.h>
using namespace std;

/* Function to sort an array using insertion sort*/
void insertionSort(int arr[], int n)
{
       int i, key, j;
       for (i = 1; i < n; i++)
       {
              key = arr[i];
              j = i - 1;

              /* Move elements of arr[0..i-1], that are
              greater than key, to one position ahead
              of their current position */
              while (j >= 0 && arr[j] > key)
              {
                     arr[j + 1] = arr[j];
                     j = j - 1;
              }
              arr[j + 1] = key;
       }
}

// A utility function ot print an array of size n
void printArray(int arr[], int n)
{
       int i;
       for (i = 0; i < n; i++)
              cout << arr[i] << endl;
}



/* Driver program to test insertion sort */
int main()
{
       int arr[] = { 12, 11, 13, 5, 6 };
       int n = sizeof(arr) / sizeof(arr[0]);

       insertionSort(arr, n);
       printArray(arr, n);

       return 0;

}
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