Timsort Implementation Using C++

The Timsort algorithm is implemented using the two famous sorting techniques, Insertion and the merge sort algorithms.

The implementation of the Timsort is pretty simple we divide the whole input array, which is provided for us as input, into chunks of blocks we call runs. These runs are created to implement the two sorting techniques becomes easier. The runs are sorted using the insertion sort algorithm. After the sorting, they are combined using the combination function available in the merge sort.

C++ code

//Here, we are writing down the C++ programming language code to demonstrate
//the concept of Timsort Implementation Using C++ with its output
#include<bits/stdc++.h>
using namespace std;
const int RUN = 32;

// This function sorts the array from the left index to
// to the right index, which is of size almost RUN
void insertionSort(int arr[], int left, int right)
{
	for (int i = left + 1; i <= right; i++)
	{
		int temp = arr[i];
		int j = i - 1;
		while (j >= left && arr[j] > temp)
		{
			arr[j+1] = arr[j];
			j--;
		}
		arr[j+1] = temp;
	}
}


// this is the function we are writing to merge the sorted RUNS
void merge(int arr[], int l, int m, int r)
{
	
	
	// the original array, which is like the input to our code
// is broken into left and right arrays (two parts easy for comparison)
	int len1 = m - l + 1, len2 = r - m;
	int left[len1], right[len2];
	for (int i = 0; i < len1; i++)
		left[i] = arr[l + i];
	for (int i = 0; i < len2; i++)
		right[i] = arr[m + 1 + i];

	int i = 0;
	int j = 0;
	int k = l;

	
	
	// once the comparison part is done, we have to merge the two arrays
	// into a single large sub-array
	while (i < len1 && j < len2)
	{
		if (left[i] <= right[j])
		{
			arr[k] = left[i];
			i++;
		}
		else
		{
			arr[k] = right[j];
			j++;
		}
		k++;
	}

	
	// the below while loop copies the elements which are present to the 
	// left (if any)
	while (i < len1)
	{
		arr[k] = left[i];
		k++;
		i++;
	}

	// the below while loop copies the elements which are present to the 
	// right (if any)
	while (j < len2)
	{
		arr[k] = right[j];
		k++;
		j++;
	}
}


// below function code snippet implements the timsort algorithm
//, a combination of both insertion and merge sort algos.
void tim_Sort_(int arr[], int n)
{
	
	// Sort individual subarrays of size RUN
	// below for loop which we have created sorts the sub-arrays which are
	// made individually of the size RUN
	for (int i = 0; i < n; i+=RUN)
		insertionSort(arr, i, min((i+RUN-1),
									(n-1)));


	
	// the runs which we have created from size 32 will merge to form
	// the size of nearly 64 to 128 and 256, and it goes on ...
	for (int size = RUN; size < n;
							size = 2*size)
	{
		
		// picking the starting of the left sub-array
		// then it will be increased by two (*2)
		for (int left = 0; left < n;
							left += 2*size)
		{
			
			
			// below are small code snippets to help us with 
			// rearrangement of the left and right sub-array indices from 
			// starting and ending
			int mid = left + size - 1;
			int right = min((left + 2*size - 1),
											(n-1));

			
			// below code helps us with the recombining of the runs using
			// the merge sort functionality
			if(mid < right)
				merge(arr, left, mid, right);
		}
	}
}

// below function prints the array created
void print_Array_(int arr[], int n)
{
	for (int i = 0; i < n; i++)
		printf("%d ", arr[i]);
	printf("\n");
}

// below, we are writing down the drive code for timsort
int main()
{
	int arr[] = {-12, 17, 15, -14, 0, 15, 0, 17, -17,
					-14, -13, 15, 18, -14, 12};
	int n = sizeof(arr)/sizeof(arr[0]);
	printf("the given array as input is : \n");
	print_Array_(arr, n);

	// calling the timsort function to perform its task
	tim_Sort_(arr, n);

	printf("Array after implementing the sorting : \n");
	print_Array_(arr, n);
	return 0;
}

Output:

the given array as input is : 
-12 17 15 -14 0 15 0 17 -17 -14 -13 15 18 -14 12 
Array after implementing the sorting : 
-17 -14 -14 -14 -13 -12 0 0 12 15 15 15 17 17 18

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