Related Articles

# Sort an array when two halves are sorted

• Difficulty Level : Easy
• Last Updated : 07 Sep, 2021

Given an integer array of which both first half and second half are sorted. Task is to merge two sorted halves of array into single sorted array.

Examples:

```Input : A[] = { 2, 3, 8, -1, 7, 10 }
Output : -1, 2, 3, 7, 8, 10

Input : A[] = {-4, 6, 9, -1, 3 }
Output : -4, -1, 3, 6, 9```

Method 1: A Simple Solution is to sort the array using built in functions (generally an implementation of quick sort).
Below is the implementation of above method:

## C++

 `// C++ program to Merge two sorted halves of``// array Into Single Sorted Array``#include ``using` `namespace` `std;` `void` `mergeTwoHalf(``int` `A[], ``int` `n)``{``    ``// Sort the given array using sort STL``    ``sort(A, A + n);``}` `// Driver code``int` `main()``{``    ``int` `A[] = { 2, 3, 8, -1, 7, 10 };``    ``int` `n = ``sizeof``(A) / ``sizeof``(A);``    ``mergeTwoHalf(A, n);` `    ``// Print sorted Array``    ``for` `(``int` `i = 0; i < n; i++)``        ``cout << A[i] << ``" "``;``    ``return` `0;``}`

## Java

 `// Java program to Merge two sorted halves of``// array Into Single Sorted Array``import` `java.io.*;``import` `java.util.*;` `class` `GFG {` `    ``static` `void` `mergeTwoHalf(``int``[] A, ``int` `n)``    ``{``        ``// Sort the given array using sort STL``        ``Arrays.sort(A);``    ``}` `    ``// Driver code``    ``static` `public` `void` `main(String[] args)``    ``{``        ``int``[] A = { ``2``, ``3``, ``8``, -``1``, ``7``, ``10` `};``        ``int` `n = A.length;``        ``mergeTwoHalf(A, n);` `        ``// Print sorted Array``        ``for` `(``int` `i = ``0``; i < n; i++)``            ``System.out.print(A[i] + ``" "``);``    ``}``}` `// This code is contributed by vt_m .`

## Python

 `# Python program to Merge two sorted``# halves of array Into Single Sorted Array`  `def` `mergeTwoHalf(A, n):` `    ``# Sort the given array using sort STL``    ``A.sort()`  `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ``A ``=` `[``2``, ``3``, ``8``, ``-``1``, ``7``, ``10``]``    ``n ``=` `len``(A)``    ``mergeTwoHalf(A, n)` `    ``# Print sorted Array``    ``for` `i ``in` `range``(n):``        ``print``(A[i], end``=``" "``)` `# This code is contributed by 29AjayKumar`

## C#

 `// C# program to Merge two sorted halves of``// array Into Single Sorted Array``using` `System;` `class` `GFG {` `    ``static` `void` `mergeTwoHalf(``int``[] A, ``int` `n)``    ``{``        ``// Sort the given array using sort STL``        ``Array.Sort(A);``    ``}` `    ``// Driver code``    ``static` `public` `void` `Main()``    ``{``        ``int``[] A = { 2, 3, 8, -1, 7, 10 };``        ``int` `n = A.Length;``        ``mergeTwoHalf(A, n);` `        ``// Print sorted Array``        ``for` `(``int` `i = 0; i < n; i++)``            ``Console.Write(A[i] + ``" "``);``    ``}``}` `// This code is contributed by vt_m .`

## PHP

 ``

## Javascript

 ``
Output
`-1 2 3 7 8 10`

Time Complexity: best & average case, worst case (for quicksort)

Space Complexity: to depending on the case & implementation (for quicksort)

For more details, check out the GFG article on Quicksort.

Method 2: A more efficient solution is to use an auxiliary array which is very similar to the Merge Function of Merge sort

Below is the implementation of above approach :

## C++

 `// C++ program to Merge Two Sorted Halves Of``// Array Into Single Sorted Array``#include ``using` `namespace` `std;` `// Merge two sorted halves of Array into single``// sorted array``void` `mergeTwoHalf(``int` `A[], ``int` `n)``{``    ``int` `half_i = 0; ``// starting index of second half` `    ``// Temp Array store sorted resultant array``    ``int` `temp[n];` `    ``// First Find the point where array is divide``    ``// into two half``    ``for` `(``int` `i = 0; i < n - 1; i++) {``        ``if` `(A[i] > A[i + 1]) {``            ``half_i = i + 1;``            ``break``;``        ``}``    ``}` `    ``// If Given array is all-ready sorted``    ``if` `(half_i == 0)``        ``return``;` `    ``// Merge two sorted arrays in single sorted array``    ``int` `i = 0, j = half_i, k = 0;``    ``while` `(i < half_i && j < n) {``        ``if` `(A[i] < A[j])``            ``temp[k++] = A[i++];``        ``else``            ``temp[k++] = A[j++];``    ``}` `    ``// Copy the remaining elements of A[i to half_! ]``    ``while` `(i < half_i)``        ``temp[k++] = A[i++];` `    ``// Copy the remaining elements of A[ half_! to n ]``    ``while` `(j < n)``        ``temp[k++] = A[j++];` `    ``for` `(``int` `i = 0; i < n; i++)``        ``A[i] = temp[i];``}` `// Driver code``int` `main()``{``    ``int` `A[] = { 2, 3, 8, -1, 7, 10 };``    ``int` `n = ``sizeof``(A) / ``sizeof``(A);``    ``mergeTwoHalf(A, n);` `    ``// Print sorted Array``    ``for` `(``int` `i = 0; i < n; i++)``        ``cout << A[i] << ``" "``;``    ``return` `0;``}`

## Java

 `// Java program to Merge Two Sorted Halves Of``// Array Into Single Sorted Array``import` `java.io.*;` `class` `GFG {` `    ``// Merge two sorted halves of Array``    ``// into single sorted array``    ``static` `void` `mergeTwoHalf(``int``[] A, ``int` `n)``    ``{``        ``int` `half_i = ``0``; ``// starting index of second half``        ``int` `i;` `        ``// Temp Array store sorted resultant array``        ``int``[] temp = ``new` `int``[n];` `        ``// First Find the point where array is divide``        ``// into two half``        ``for` `(i = ``0``; i < n - ``1``; i++) {``            ``if` `(A[i] > A[i + ``1``]) {``                ``half_i = i + ``1``;``                ``break``;``            ``}``        ``}` `        ``// If Given array is all-ready sorted``        ``if` `(half_i == ``0``)``            ``return``;` `        ``// Merge two sorted arrays in single sorted array``        ``i = ``0``;``        ``int` `j = half_i;``        ``int` `k = ``0``;``        ``while` `(i < half_i && j < n) {``            ``if` `(A[i] < A[j])``                ``temp[k++] = A[i++];``            ``else``                ``temp[k++] = A[j++];``        ``}` `        ``// Copy the remaining elements of A[i to half_! ]``        ``while` `(i < half_i)``            ``temp[k++] = A[i++];` `        ``// Copy the remaining elements of A[ half_! to n ]``        ``while` `(j < n)``            ``temp[k++] = A[j++];` `        ``for` `(i = ``0``; i < n; i++)``            ``A[i] = temp[i];``    ``}` `    ``// Driver code``    ``static` `public` `void` `main(String[] args)``    ``{``        ``int``[] A = { ``2``, ``3``, ``8``, -``1``, ``7``, ``10` `};``        ``int` `n = A.length;``        ``mergeTwoHalf(A, n);` `        ``// Print sorted Array``        ``for` `(``int` `i = ``0``; i < n; i++)``            ``System.out.print(A[i] + ``" "``);``    ``}``}` `// This code is contributed by vt_m .`

## Python3

 `# Python3 program to Merge Two Sorted Halves Of``# Array Into Single Sorted Array` `# Merge two sorted halves of Array into single``# sorted array``def` `mergeTwoHalf(A, n):``    ` `    ``# Starting index of second half``    ``half_i ``=` `0`    `    ``# Temp Array store sorted resultant array``    ``temp ``=` `[``0` `for` `i ``in` `range``(n)]` `    ``# First Find the point where array is``    ``# divide into two half``    ``for` `i ``in` `range``(n ``-` `1``):``        ``if` `(A[i] > A[i ``+` `1``]):``            ``half_i ``=` `i ``+` `1``            ``break` `    ``# If Given array is all-ready sorted``    ``if` `(half_i ``=``=` `0``):``        ``return` `    ``# Merge two sorted arrays in single``    ``# sorted array``    ``i ``=` `0``    ``j ``=` `half_i``    ``k ``=` `0``    ` `    ``while` `(i < half_i ``and` `j < n):``        ``if` `(A[i] < A[j]):``            ``temp[k] ``=` `A[i]``            ``k ``+``=` `1``            ``i ``+``=` `1``        ``else``:``            ``temp[k] ``=` `A[j]``            ``k ``+``=` `1``            ``j ``+``=` `1``    ` `    ``# Copy the remaining elements of A[i to half_! ]``    ``while` `i < half_i:``        ``temp[k] ``=` `A[i]``        ``k ``+``=` `1``        ``i ``+``=` `1` `    ``# Copy the remaining elements of A[ half_! to n ]``    ``while` `(j < n):``        ``temp[k] ``=` `A[j]``        ``k ``+``=` `1``        ``j ``+``=` `1` `    ``for` `i ``in` `range``(n):``        ``A[i] ``=` `temp[i]` `# Driver code``A ``=` `[ ``2``, ``3``, ``8``, ``-``1``, ``7``, ``10` `]``n ``=` `len``(A)` `mergeTwoHalf(A, n)` `# Print sorted Array``print``(``*``A, sep ``=` `' '``)` `# This code is contributed by avanitrachhadiya2155`

## C#

 `// C# program to Merge Two Sorted Halves Of``// Array Into Single Sorted Array``using` `System` `    ``class` `GFG {` `    ``// Merge two sorted halves of Array``    ``// into single sorted array``    ``static` `void` `mergeTwoHalf(``int``[] A, ``int` `n)``    ``{``        ``int` `half_i = 0``            ``// starting index of second half``            ``int` `i` `            ``// Temp Array store sorted resultant array``            ``int``[] temp``            ``= ``new` `int``[n]` `            ``// First Find the point where array is divide``            ``// into two half``            ``for` `(i = 0 i < n - 1 i++)``        ``{``            ``if` `(A[i] > A[i + 1]) {``                ``half_i = i + 1 ``break``            ``}``        ``}` `        ``// If Given array is all-ready sorted``        ``if` `(half_i == 0)``            ``return` `                ``// Merge two sorted arrays in single sorted``                ``// array``                ``i = 0 ``int` `j = half_i ``int` `k``                ``= 0 ``while` `(i < half_i & &j < n)``            ``{``                ``if` `(A[i] < A[j])``                    ``temp[k++] = A[i++] ``else` `temp[k++]``                        ``= A[j++]``            ``}` `        ``// Copy the remaining elements of A[i to half_!]``        ``while` `(i < half_i)``            ``temp[k++] = A[i++]` `                ``// Copy the remaining elements of A[half_!``                ``// to n]``                ``while` `(j < n) temp[k++]``                ``= A[j++]` `                ``for` `(i = 0 i < n i++) A[i]``                ``= temp[i]``    ``}` `    ``// Driver code``    ``static` `public` `void` `Main()``    ``{``        ``int``[] A``            ``= { 2,``                ``3,``                ``8,``                ``-1,``                ``7,``                ``10 } ``int` `n``            ``= A.Length mergeTwoHalf(A, n)` `              ``// Print sorted Array``              ``for` `(``int` `i = 0 i < n i++)``                  ``Console.Write(A[i] + ``" "``)``    ``}``}` `// This code is contributed by vt_m .`

## Javascript

 ``
Output
`-1 2 3 7 8 10`

Time Complexity: Space Complexity: Reference: https://www.careercup.com/question?id=8412257

If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

My Personal Notes arrow_drop_up