TimSort - GeeksforGeeks

TimSort

Difficulty Level : Medium
Last Updated : 12 Oct, 2020

TimSort is a sorting algorithm based on Insertion Sort and Merge Sort.

A stable sorting algorithm works in O(n Log n) time
Used in Java’s Arrays.sort() as well as Python’s sorted() and sort().
First sort small pieces using Insertion Sort, then merges the pieces using merge of merge sort.

We divide the Array into blocks known as Run. We sort those runs using insertion sort one by one and then merge those runs using the combine function used in merge sort. If the size of the Array is less than run, then Array gets sorted just by using Insertion Sort. The size of the run may vary from 32 to 64 depending upon the size of the array. Note that the merge function performs well when size subarrays are powers of 2. The idea is based on the fact that insertion sort performs well for small arrays.

Details of below implementation:

We consider size of run as 32.
We one by one sort pieces of size equal to run
After sorting individual pieces, we merge them one by one. We double the size of merged subarrays after every iteration.

C++

// C++ program to perform TimSort. 
#include<bits/stdc++.h> 
using namespace std; 
const int RUN = 32; 
  
// This function sorts array from left index to 
// to right index which is of size atmost 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; 
    } 
} 
  
// Merge function merges the sorted runs 
void merge(int arr[], int l, int m, int r) 
{ 
      
    // Original array is broken in two parts 
    // left and right array 
    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; 
  
    // After comparing, we  
    // merge those two array 
    // in larger sub array 
    while (i < len1 && j < len2) 
    { 
        if (left[i] <= right[j]) 
        { 
            arr[k] = left[i]; 
            i++; 
        } 
        else
        { 
            arr[k] = right[j]; 
            j++; 
        } 
        k++; 
    } 
  
    // Copy remaining elements of left, if any 
    while (i < len1) 
    { 
        arr[k] = left[i]; 
        k++; 
        i++; 
    } 
  
    // Copy remaining element of right, if any 
    while (j < len2) 
    { 
        arr[k] = right[j]; 
        k++; 
        j++; 
    } 
} 
  
// Iterative Timsort function to sort the 
// array[0...n-1] (similar to merge sort) 
void timSort(int arr[], int n) 
{ 
      
    // Sort individual subarrays of size RUN 
    for (int i = 0; i < n; i+=RUN) 
        insertionSort(arr, i, min((i+31),  
                                    (n-1))); 
  
    // Start merging from size RUN (or 32).  
    // It will merge 
    // to form size 64, then 128, 256  
    // and so on .... 
    for (int size = RUN; size < n;  
                             size = 2*size) 
    { 
          
        // pick starting point of  
        // left sub array. We 
        // are going to merge  
        // arr[left..left+size-1] 
        // and arr[left+size, left+2*size-1] 
        // After every merge, we  
        // increase left by 2*size 
        for (int left = 0; left < n;  
                             left += 2*size) 
        { 
              
            // find ending point of  
            // left sub array 
            // mid+1 is starting point  
            // of right sub array 
            int mid = left + size - 1; 
            int right = min((left + 2*size - 1),  
                                            (n-1)); 
  
            // merge sub array arr[left.....mid] & 
            // arr[mid+1....right] 
            merge(arr, left, mid, right); 
        } 
    } 
} 
  
// Utility function to print the Array 
void printArray(int arr[], int n) 
{ 
    for (int i = 0; i < n; i++) 
        printf("%d  ", arr[i]); 
    printf("\n"); 
} 
  
// Driver program to test above function 
int main() 
{ 
    int arr[] = {-2, 7, 15, -14, 0, 15, 0, 7, -7,  
                       -4, -13, 5, 8, -14, 12}; 
    int n = sizeof(arr)/sizeof(arr[0]); 
    printf("Given Array is\n"); 
    printArray(arr, n); 
  
    // Function Call 
    timSort(arr, n); 
  
    printf("After Sorting Array is\n"); 
    printArray(arr, n); 
    return 0; 
} 

Java

// Java program to perform TimSort. 
class GFG  
{ 
  
    static int MIN_MERGE = 32; 
  
    public static int minRunLength(int n) 
    { 
        assert n >= 0; 
        
        // Becomes 1 if any 1 bits are shifted off 
        int r = 0; 
        while (n >= MIN_MERGE)  
        { 
            r |= (n & 1); 
            n >>= 1; 
        } 
        return n + r; 
    } 
  
    // This function sorts array from left index to 
    // to right index which is of size atmost RUN 
    public static 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; 
        } 
    } 
  
    // Merge function merges the sorted runs 
    public static void merge(int[] arr, int l,  
                                 int m, int r) 
    { 
        // Original array is broken in two parts 
        // left and right array 
        int len1 = m - l + 1, len2 = r - m; 
        int[] left = new int[len1]; 
        int[] right = new int[len2]; 
        for (int x = 0; x < len1; x++)  
        { 
            left[x] = arr[l + x]; 
        } 
        for (int x = 0; x < len2; x++)  
        { 
            right[x] = arr[m + 1 + x]; 
        } 
  
        int i = 0; 
        int j = 0; 
        int k = l; 
  
        // After comparing, we merge those two array 
        // in larger sub array 
        while (i < len1 && j < len2)  
        { 
            if (left[i] <= right[j])  
            { 
                arr[k] = left[i]; 
                i++; 
            } 
            else { 
                arr[k] = right[j]; 
                j++; 
            } 
            k++; 
        } 
  
        // Copy remaining elements  
        // of left, if any 
        while (i < len1)  
        { 
            arr[k] = left[i]; 
            k++; 
            i++; 
        } 
  
        // Copy remaining element  
        // of right, if any 
        while (j < len2)  
        { 
            arr[k] = right[j]; 
            k++; 
            j++; 
        } 
    } 
  
    // Iterative Timsort function to sort the 
    // array[0...n-1] (similar to merge sort) 
    public static void timSort(int[] arr, int n) 
    { 
        int minRun = minRunLength(MIN_MERGE); 
        
        // Sort individual subarrays of size RUN 
        for (int i = 0; i < n; i += minRun) 
        { 
            insertionSort(arr, i, 
                          Math.min((i + 31), (n - 1))); 
        } 
  
        // Start merging from size  
        // RUN (or 32). It will 
        // merge to form size 64,  
        // then 128, 256 and so on 
        // .... 
        for (int size = minRun; size < n; size = 2 * size)  
        { 
  
            // Pick starting point  
            // of left sub array. We 
            // are going to merge  
            // arr[left..left+size-1] 
            // and arr[left+size, left+2*size-1] 
            // After every merge, we  
            // increase left by 2*size 
            for (int left = 0; left < n;  
                                 left += 2 * size)  
            { 
  
                // Find ending point of left sub array 
                // mid+1 is starting point of right sub 
                // array 
                int mid = left + size - 1; 
                int right = Math.min((left + 2 * size - 1), 
                                     (n - 1)); 
  
                // Merge sub array arr[left.....mid] & 
                // arr[mid+1....right] 
                merge(arr, left, mid, right); 
            } 
        } 
    } 
  
    // Utility function to print the Array 
    public static void printArray(int[] arr, int n) 
    { 
        for (int i = 0; i < n; i++) { 
            System.out.print(arr[i] + " "); 
        } 
        System.out.print("\n"); 
    } 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        int[] arr = { -2, 7,  15,  -14, 0, 15,  0, 7, 
                      -7, -4, -13, 5,   8, -14, 12 }; 
        int n = arr.length; 
        System.out.println("Given Array is"); 
        printArray(arr, n); 
  
        timSort(arr, n); 
  
        System.out.println("After Sorting Array is"); 
        printArray(arr, n); 
    } 
} 
  
// This code has been contributed by 29AjayKumar

Python3

# Python3 program to perform basic timSort 
MIN_MERGE = 32
  
def calcMinRun(n): 
    """Returns the minimum length of a  
    run from 23 - 64 so that 
    the len(array)/minrun is less than or  
    equal to a power of 2. 
  
    e.g. 1=>1, ..., 63=>63, 64=>32, 65=>33,  
    ..., 127=>64, 128=>32, ... 
    """
    r = 0
    while n >= MIN_MERGE: 
        r |= n & 1
        n >>= 1
    return n + r 
  
  
# This function sorts array from left index to 
# to right index which is of size atmost RUN 
def insertionSort(arr, left, right): 
    for i in range(left + 1, right + 1): 
        j = i 
        while j > left and arr[j] < arr[j - 1]: 
            arr[j], arr[j - 1] = arr[j - 1], arr[j] 
            j -= 1
  
  
# Merge function merges the sorted runs 
def merge(arr, l, m, r): 
      
    # original array is broken in two parts 
    # left and right array 
    len1, len2 = m - l + 1, r - m 
    left, right = [], [] 
    for i in range(0, len1): 
        left.append(arr[l + i]) 
    for i in range(0, len2): 
        right.append(arr[m + 1 + i]) 
  
    i, j, k = 0, 0, l 
      
    # after comparing, we merge those two array 
    # in larger sub array 
    while i < len1 and j < len2: 
        if left[i] <= right[j]: 
            arr[k] = left[i] 
            i += 1
  
        else: 
            arr[k] = right[j] 
            j += 1
  
        k += 1
  
    # Copy remaining elements of left, if any 
    while i < len1: 
        arr[k] = left[i] 
        k += 1
        i += 1
  
    # Copy remaining element of right, if any 
    while j < len2: 
        arr[k] = right[j] 
        k += 1
        j += 1
  
  
# Iterative Timsort function to sort the 
# array[0...n-1] (similar to merge sort) 
def timSort(arr): 
    n = len(arr) 
    minRun = calcMinRun(n) 
      
    # Sort individual subarrays of size RUN 
    for start in range(0, n, minRun): 
        end = min(start + minRun - 1, n - 1) 
        insertionSort(arr, start, end) 
  
    # Start merging from size RUN (or 32). It will merge 
    # to form size 64, then 128, 256 and so on .... 
    size = minRun 
    while size < n: 
          
        # Pick starting point of left sub array. We 
        # are going to merge arr[left..left+size-1] 
        # and arr[left+size, left+2*size-1] 
        # After every merge, we increase left by 2*size 
        for left in range(0, n, 2 * size): 
  
            # Find ending point of left sub array 
            # mid+1 is starting point of right sub array 
            mid = min(n - 1, left + size - 1) 
            right = min((left + 2 * size - 1), (n - 1)) 
  
            # Merge sub array arr[left.....mid] & 
            # arr[mid+1....right] 
            merge(arr, left, mid, right) 
  
        size = 2 * size 
  
  
# Driver program to test above function 
if __name__ == "__main__": 
  
    arr = [-2, 7, 15, -14, 0, 15, 0,  
           7, -7, -4, -13, 5, 8, -14, 12] 
  
    print("Given Array is") 
    print(arr) 
  
    # Function Call 
    timSort(arr) 
  
    print("After Sorting Array is") 
    print(arr) 
    # [-14, -14, -13, -7, -4, -2, 0, 0,  
           5, 7, 7, 8, 12, 15, 15] 

C#

// C# program to perform TimSort.  
using System;  
   
class GFG  
{  
    public const int RUN = 32; 
      
    // This function sorts array from left index to  
    // to right index which is of size atmost RUN  
    public static 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;  
        }  
    }  
        
    // merge function merges the sorted runs  
    public static void merge(int[] arr, int l,  
                                   int m, int r)  
    {  
        // original array is broken in two parts  
        // left and right array  
        int len1 = m - l + 1, len2 = r - m;  
        int[] left = new int[len1]; 
        int[] right = new int[len2];  
        for (int x = 0; x < len1; x++) 
            left[x] = arr[l + x];  
        for (int x = 0; x < len2; x++)  
            right[x] = arr[m + 1 + x];  
        
        int i = 0;  
        int j = 0;  
        int k = l;  
        
        // After comparing, we merge those two array  
        // in larger sub array  
        while (i < len1 && j < len2)  
        {  
            if (left[i] <= right[j])  
            {  
                arr[k] = left[i];  
                i++;  
            }  
            else
            {  
                arr[k] = right[j];  
                j++;  
            }  
            k++;  
        }  
        
        // Copy remaining elements  
        // of left, if any  
        while (i < len1)  
        {  
            arr[k] = left[i];  
            k++;  
            i++;  
        }  
        
        // Copy remaining element  
        // of right, if any  
        while (j < len2)  
        {  
            arr[k] = right[j];  
            k++;  
            j++;  
        }  
    }  
        
    // Iterative Timsort function to sort the  
    // array[0...n-1] (similar to merge sort)  
    public static void timSort(int[] arr, int n)  
    {  
          
        // Sort individual subarrays of size RUN  
        for (int i = 0; i < n; i+=RUN)  
            insertionSort(arr, i,  
                         Math.Min((i+31), (n-1)));  
        
        // Start merging from size RUN (or 32).  
        // It will merge  
        // to form size 64, then  
        // 128, 256 and so on ....  
        for (int size = RUN; size < n;  
                                 size = 2*size)  
        {  
              
            // Pick starting point of  
            // left sub array. We  
            // are going to merge  
            // arr[left..left+size-1]  
            // and arr[left+size, left+2*size-1]  
            // After every merge, we increase  
            // left by 2*size  
            for (int left = 0; left < n;  
                                  left += 2*size)  
            {  
                  
                // Find ending point of left sub array  
                // mid+1 is starting point of  
                // right sub array  
                int mid = left + size - 1;  
                int right = Math.Min((left +  
                                    2*size - 1), (n-1));  
        
                // Merge sub array arr[left.....mid] &  
                // arr[mid+1....right]  
                merge(arr, left, mid, right);  
            }  
        }  
    }  
        
    // Utility function to print the Array  
    public static void printArray(int[] arr, int n)  
    {  
        for (int i = 0; i < n; i++)  
            Console.Write(arr[i] + " ");  
        Console.Write("\n");  
    }  
        
    // Driver program to test above function 
    public static void Main() 
    { 
        int[] arr = {-2, 7, 15, -14, 0, 15, 0,  
                   7, -7, -4, -13, 5, 8, -14, 12};  
        int n = arr.Length; 
        Console.Write("Given Array is\n");  
        printArray(arr, n);  
        
        // Function Call 
        timSort(arr, n);  
        
        Console.Write("After Sorting Array is\n");  
        printArray(arr, n);  
    }     
} 
  
//This code is contributed by DrRoot_

Output:

Given Array is
-2, 7, 15, -14, 0, 15, 0, 7, -7, -4, -13, 5, 8, -14, 12
After Sorting Array is
-14  -14  -13  -7  -4  -2  0  0  5  7  7  8  12  15  15

References :
https://svn.python.org/projects/python/trunk/Objects/listsort.txt
https://en.wikipedia.org/wiki/Timsort#Minimum_size_.28minrun.29
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