Merging two unsorted arrays in sorted order

27 Jan, 2022
Write a SortedMerge() function that takes two lists, each of which is unsorted, and merges the two together into one new list which is in sorted (increasing) order. SortedMerge() should return the new list.
Examples : 
Input : a[] = {10, 5, 15}
        b[] = {20, 3, 2}
Output : Merge List :
        {2, 3, 5, 10, 15, 20}

Input : a[] = {1, 10, 5, 15}
        b[] = {20, 0, 2}
Output : Merge List :
        {0, 1, 2, 5, 10, 15, 20}
There are many cases to deal with: either ‘a’ or ‘b’ may be empty, during processing either ‘a’ or ‘b’ may run out first, and finally, there’s the problem of starting the result list empty and building it up while going through ‘a’ and ‘b’.
Method 1 (first Concatenate then Sort)
In this case, we first append the two unsorted lists. Then we simply sort the concatenated list. 
C++
Java
Python3
C#
PHP
Javascript
// CPP program to merge two unsorted lists// in sorted order#include <bits/stdc++.h>using namespace std; // Function to merge array in sorted ordervoid sortedMerge(int a[], int b[], int res[],                                int n, int m){    // Concatenate two arrays    int i = 0, j = 0, k = 0;    while (i < n) {        res[k] = a[i];        i += 1;        k += 1;    }    while (j < m) {        res[k] = b[j];        j += 1;        k += 1;    }     // sorting the res array    sort(res, res + n + m);} // Driver codeint main(){    int a[] = { 10, 5, 15 };    int b[] = { 20, 3, 2, 12 };    int n = sizeof(a) / sizeof(a[0]);    int m = sizeof(b) / sizeof(b[0]);     // Final merge list    int res[n + m];    sortedMerge(a, b, res, n, m);     cout << "Sorted merged list :";    for (int i = 0; i < n + m; i++)        cout << " " << res[i];    cout << "n";     return 0;}
// Java Code for Merging two unsorted// arrays in sorted orderimport java.util.*; class GFG {     // Function to merge array in sorted order    public static void sortedMerge(int a[], int b[],                                   int res[], int n,                                   int m)    {        // Concatenate two arrays        int i = 0, j = 0, k = 0;        while (i < n) {            res[k] = a[i];            i++;            k++;        }                 while (j < m) {            res[k] = b[j];            j++;            k++;        }             // sorting the res array        Arrays.sort(res);    }         /* Driver program to test above function */    public static void main(String[] args)    {        int a[] = { 10, 5, 15 };        int b[] = { 20, 3, 2, 12 };        int n = a.length;        int m = b.length;             // Final merge list        int res[]=new int[n + m];        sortedMerge(a, b, res, n, m);             System.out.print("Sorted merged list :");        for (int i = 0; i < n + m; i++)            System.out.print(" " + res[i]);    }} // This code is contributed by Arnav Kr. Mandal.
# Python program to merge two unsorted lists# in sorted order # Function to merge array in sorted orderdef sortedMerge(a, b, res, n, m):    # Concatenate two arrays    i, j, k = 0, 0, 0    while (i < n):        res[k] = a[i]        i += 1        k += 1    while (j < m):        res[k] = b[j]        j += 1        k += 1      # sorting the res array    res.sort()  # Driver codea = [ 10, 5, 15 ]b = [ 20, 3, 2, 12 ]n = len(a)m = len(b) # Final merge listres = [0 for i in range(n + m)]sortedMerge(a, b, res, n, m)print ("Sorted merged list :")for i in range(n + m):    print(res[i],end=" ")     # This code is contributed by Sachin Bisht   
// C# Code for Merging two// unsorted arrays in sorted orderusing System; class GFG {     // Function to merge array in sorted order    public static void sortedMerge(int []a, int []b,                                   int []res, int n,                                   int m)    {        // Concatenate two arrays        int i = 0, j = 0, k = 0;        while (i < n) {            res[k] = a[i];            i++;            k++;        }                 while (j < m) {            res[k] = b[j];            j++;            k++;        }             // sorting the res array        Array.Sort(res);    }         /* Driver program to test above function */    public static void Main()    {        int []a = {10, 5, 15};        int []b = {20, 3, 2, 12};        int n = a.Length;        int m = b.Length;             // Final merge list        int []res=new int[n + m];        sortedMerge(a, b, res, n, m);             Console.Write("Sorted merged list :");        for (int i = 0; i < n + m; i++)            Console.Write(" " + res[i]);    }} // This code is contributed by nitin mittal.
<?php// PHP program to merge two unsorted lists// in sorted order // Function to merge array in sorted orderfunction sortedMerge($a, $b, $n, $m){    // Concatenate two arrays    $res = array();    $i = 0; $j = 0; $k = 0;    while ($i < $n)    {        $res[$k] = $a[$i];        $i += 1;        $k += 1;    }    while ($j < $m)    {        $res[$k] = $b[$j];        $j += 1;        $k += 1;    }     // sorting the res array    sort($res);    echo "Sorted merged list :";         for ($i = 0; $i < count($res); $i++)        echo $res[$i] . " ";} // Driver code$a = array( 10, 5, 15 );$b = array( 20, 3, 2, 12 );$n = count($a);$m = count($b); // Final merge list sortedMerge($a, $b, $n, $m); // This code is contributed by Rajput-Ji.?>
<script> // Javascript program to merge two unsorted lists// in sorted order // Function to merge array in sorted orderfunction sortedMerge(a, b, res,                                n, m){    // Sorting a[] and b[]    a.sort((a,b) => a-b);    b.sort((a,b) => a-b);     // Merge two sorted arrays into res[]    let i = 0, j = 0, k = 0;    while (i < n && j < m) {        if (a[i] <= b[j]) {            res[k] = a[i];            i += 1;            k += 1;        } else {            res[k] = b[j];            j += 1;            k += 1;        }    }       while (i < n) { // Merging remaining                    // elements of a[] (if any)        res[k] = a[i];        i += 1;        k += 1;    }       while (j < m) { // Merging remaining                    // elements of b[] (if any)        res[k] = b[j];        j += 1;        k += 1;    }} // Driver code     let a = [ 10, 5, 15 ];    let b = [ 20, 3, 2, 12 ];    let n = a.length;    let m = b.length;     // Final merge list    let res = new Array(n + m);     sortedMerge(a, b, res, n, m);     document.write("Sorted merge list :");    for (let i = 0; i < n + m; i++)        document.write(" " + res[i]);  //This code is contributed by Mayank Tyagi</script>
Output:  
Sorted merged list : 2 3 5 10 12 15 20
Time Complexity: O ( (n + m) (log(n + m)) ) Auxiliary Space: O ( (n + m) ) 
Method 2 (First Sort then Merge)
We first sort both the given arrays separately. Then we simply merge two sorted arrays.  
C++
Java
Python3
C#
Javascript
// CPP program to merge two unsorted lists// in sorted order#include <bits/stdc++.h>using namespace std; // Function to merge array in sorted ordervoid sortedMerge(int a[], int b[], int res[],                                int n, int m){    // Sorting a[] and b[]    sort(a, a + n);    sort(b, b + m);     // Merge two sorted arrays into res[]    int i = 0, j = 0, k = 0;    while (i < n && j < m) {        if (a[i] <= b[j]) {            res[k] = a[i];            i += 1;            k += 1;        } else {            res[k] = b[j];            j += 1;            k += 1;        }    }       while (i < n) {  // Merging remaining                     // elements of a[] (if any)        res[k] = a[i];        i += 1;        k += 1;    }       while (j < m) {   // Merging remaining                     // elements of b[] (if any)        res[k] = b[j];        j += 1;        k += 1;    }} // Driver codeint main(){    int a[] = { 10, 5, 15 };    int b[] = { 20, 3, 2, 12 };    int n = sizeof(a) / sizeof(a[0]);    int m = sizeof(b) / sizeof(b[0]);     // Final merge list    int res[n + m];     sortedMerge(a, b, res, n, m);     cout << "Sorted merge list :";    for (int i = 0; i < n + m; i++)        cout << " " << res[i];    cout << "n";     return 0;}
// JAVA Code for Merging two unsorted// arrays in sorted orderimport java.util.*; class GFG {         // Function to merge array in sorted order    public static void sortedMerge(int a[], int b[],                                  int res[], int n,                                            int m)    {        // Sorting a[] and b[]        Arrays.sort(a);        Arrays.sort(b);              // Merge two sorted arrays into res[]        int i = 0, j = 0, k = 0;        while (i < n && j < m) {            if (a[i] <= b[j]) {                res[k] = a[i];                i += 1;                k += 1;            } else {                res[k] = b[j];                j += 1;                k += 1;            }        }                    while (i < n) {  // Merging remaining                         // elements of a[] (if any)            res[k] = a[i];            i += 1;            k += 1;        }           while (j < m) {   // Merging remaining                         // elements of b[] (if any)            res[k] = b[j];            j += 1;            k += 1;        }    }         /* Driver program to test above function */    public static void main(String[] args)    {        int a[] = { 10, 5, 15 };        int b[] = { 20, 3, 2, 12 };        int n = a.length;        int m = b.length;              // Final merge list        int res[] = new int[n + m];        sortedMerge(a, b, res, n, m);              System.out.print( "Sorted merged list :");        for (int i = 0; i < n + m; i++)            System.out.print(" " + res[i]);      }}// This code is contributed by Arnav Kr. Mandal.
# Python program to merge two unsorted lists# in sorted order # Function to merge array in sorted orderdef sortedMerge(a, b, res, n, m):    # Sorting a[] and b[]    a.sort()    b.sort()         # Merge two sorted arrays into res[]    i, j, k = 0, 0, 0    while (i < n and j < m):        if (a[i] <= b[j]):            res[k] = a[i]            i += 1            k += 1        else:            res[k] = b[j]            j += 1            k += 1                 while (i < n):  # Merging remaining                    # elements of a[] (if any)        res[k] = a[i]        i += 1        k += 1             while (j < m):  # Merging remaining                    # elements of b[] (if any)        res[k] = b[j]        j += 1        k += 1  # Driver codea = [ 10, 5, 15 ]b = [ 20, 3, 2, 12 ]n = len(a)m = len(b) # Final merge listres = [0 for i in range(n + m)]sortedMerge(a, b, res, n, m)print ("Sorted merged list :")for i in range(n + m):    print(res[i],end=" ")     # This code is contributed by Sachin Bisht   
// C# Code for Merging two unsorted// arrays in sorted orderusing System; class GFG {         // Function to merge array in    // sorted order    static void sortedMerge(int []a, int []b,                     int []res, int n, int m)    {                 // Sorting a[] and b[]        Array.Sort(a);        Array.Sort(b);             // Merge two sorted arrays into res[]        int i = 0, j = 0, k = 0;                 while (i < n && j < m)        {            if (a[i] <= b[j])            {                res[k] = a[i];                i += 1;                k += 1;            }            else            {                res[k] = b[j];                j += 1;                k += 1;            }        }                 while (i < n)        {                         // Merging remaining            // elements of a[] (if any)            res[k] = a[i];            i += 1;            k += 1;        }        while (j < m)        {                         // Merging remaining            // elements of b[] (if any)            res[k] = b[j];            j += 1;            k += 1;        }    }         /* Driver program to test    above function */    public static void Main()    {        int []a = { 10, 5, 15 };        int []b = { 20, 3, 2, 12 };        int n = a.Length;        int m = b.Length;             // Final merge list        int []res = new int[n + m];        sortedMerge(a, b, res, n, m);             Console.Write( "Sorted merged list :");        for (int i = 0; i < n + m; i++)            Console.Write(" " + res[i]);    }} // This code is contributed by nitin mittal.
<script> // JavaScript program to merge two unsorted// lists in sorted order // Function to merge array in sorted orderfunction sortedMerge(a, b, res, n, m){         // Sorting a[] and b[]    a.sort((a, b) => a - b);    b.sort((a, b) => a - b);     // Merge two sorted arrays into res[]    let i = 0, j = 0, k = 0;    while (i < n && j < m)    {        if (a[i] <= b[j])        {            res[k] = a[i];            i += 1;            k += 1;        }        else        {            res[k] = b[j];            j += 1;            k += 1;        }    }         // Merging remaining    // elements of a[] (if any)    while (i < n)    {        res[k] = a[i];        i += 1;        k += 1;    }         // Merging remaining    // elements of b[] (if any)    while (j < m)    {        res[k] = b[j];        j += 1;        k += 1;    }} // Driver codelet a = [ 10, 5, 15 ];let b = [ 20, 3, 2, 12 ];let n = a.length;let m = b.length; // Final merge listlet res = new Array(n + m); sortedMerge(a, b, res, n, m); document.write("Sorted merge list :");for(let i = 0; i < n + m; i++)    document.write(" " + res[i]); // This code is contributed by Surbhi Tyagi. </script>
Output: 
Sorted merge list : 2 3 5 10 12 15 20
Time Complexity: O (nlogn + mlogm + (n + m)) Space Complexity: O ( (n + m) )
It is obvious from above time complexities that method 2 is better than method 1.This article is contributed by Sachin Bisht. 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.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 
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