# Sort an almost sorted array where only two elements are swapped

• Difficulty Level : Easy
• Last Updated : 23 May, 2022

Given an almost sorted array where only two elements are swapped, how to sort the array efficiently?
Examples :

Input:  arr[] = {10, 20, 60, 40, 50, 30}
// 30 and 60 are swapped
Output: arr[] = {10, 20, 30, 40, 50, 60}

Input:  arr[] = {10, 20, 40, 30, 50, 60}
// 30 and 40 are swapped
Output: arr[] = {10, 20, 30, 40, 50, 60}

Input:   arr[] = {1, 5, 3}
// 3 and 5 are swapped
Output:  arr[] = {1, 3, 5}

Expected time complexity is O(n) and only one swap operation to fix the array.

The idea is to traverse from rightmost side and find the first out of order element (element which is smaller than previous element). Once first element is found, find the other out of order element by traversing the array toward left side.
Below is implementation of above idea.

## C++

 // C++ program to sort using one swap#include#includeusing namespace std; // This function sorts an array that can be sorted// by single swapvoid sortByOneSwap(int arr[], int n){    // Traverse the given array from rightmost side    for (int i = n-1; i > 0; i--)    {        // Check if arr[i] is not in order        if (arr[i] < arr[i-1])        {            // Find the other element to be            // swapped with arr[i]            int j = i-1;            while (j>=0 && arr[i] < arr[j])                j--;             // Swap the pair            swap(arr[i], arr[j+1]);            break;        }    }} // A utility function to print an array of size nvoid printArray(int arr[], int n){    int i;    for (i=0; i < n; i++)        cout << arr[i] << " ";    cout << endl;} /* Driver program to test insertion sort */int main(){    int arr[] = {10, 30, 20, 40, 50, 60, 70};    int n = sizeof(arr)/sizeof(arr[0]);     cout << "Given array is \n";    printArray(arr, n);     sortByOneSwap(arr, n);     cout << "Sorted array is \n";    printArray(arr, n);     return 0;}

## Java

 // Java program to// sort using one swapimport java.io.*; class GFG{// This function sorts an array// that can be sorted by single swapstatic void sortByOneSwap(int arr[],                          int n){    // Traverse the given array    // from rightmost side    for (int i = n - 1; i > 0; i--)    {        // Check if arr[i]        // is not in order        if (arr[i] < arr[i - 1])        {            // Find the other element            // to be swapped with arr[i]            int j = i - 1;            while (j >= 0 && arr[i] < arr[j])                j--;             // Swap the pair            int temp = arr[i];            arr[i] = arr[j + 1];            arr[j + 1] = temp;                 break;        }    }} // A utility function to// print an array of size nstatic void printArray(int arr[], int n){    int i;    for (i = 0; i < n; i++)        System.out.print(arr[i] + " ");    System.out.println();} // Driver Codepublic static void main(String[] args){int arr[] = {10, 30, 20,             40, 50, 60, 70};int n = arr.length; System.out.println("Given array is ");printArray(arr, n); sortByOneSwap(arr, n); System.out.println("Sorted array is ");printArray(arr, n);}} // This code is contributed by anuj_67.

## Python3

 # Python program to# sort using one swap # This function sorts an array# that can be sorted by single swapdef sortByOneSwap(arr, n):       # Traverse the given array    # from rightmost side    for i in range(n - 1, 0, -1):               # Check if arr[i]        # is not in order        if (arr[i] < arr[i - 1]):                       # Find the other element            # to be swapped with arr[i]            j = i - 1;            while (j >= 0 and arr[i] < arr[j]):                j -= 1;             # Swap the pair            temp = arr[i];            arr[i] = arr[j + 1];            arr[j + 1] = temp;             break;         # A utility function to# print an array of size ndef printArray(arr, n):    for i in range(n):        print(arr[i], end = " ");    print(); # Driver Codeif __name__ == '__main__':    arr = [ 10, 30, 20, 40, 50, 60, 70 ];    n = len(arr);     print("Given array is ");    printArray(arr, n);     sortByOneSwap(arr, n);     print("Sorted array is ");    printArray(arr, n); # This code is contributed by gauravrajput1

## C#

 // C# program to sort using one swapusing System; class GFG{ // This function sorts an array// that can be sorted by single swapstatic void sortByOneSwap(int []arr,                          int n){    // Traverse the given array    // from rightmost side    for (int i = n - 1; i > 0; i--)    {        // Check if arr[i] is not in order        if (arr[i] < arr[i - 1])        {            // Find the other element to be            // swapped with arr[i]            int j = i - 1;            while (j >= 0 && arr[i] < arr[j])                j--;             // Swap the pair            int temp = arr[i];            arr[i] = arr[j + 1];            arr[j + 1] = temp;             break;        }    }} // A utility function to print an// array of size nstatic void printArray(int []arr, int n){    int i;    for (i = 0; i < n; i++)        Console.Write(arr[i] + " ");    Console.WriteLine();} // Driver Codepublic static void Main(){    int []arr = {10, 30, 20,                 40, 50, 60, 70};    int n = arr.Length;     Console.WriteLine("Given array is ");    printArray(arr, n);     sortByOneSwap(arr, n);     Console.WriteLine("Sorted array is ");    printArray(arr, n);}} // This code is contributed by 29AjayKumar

## PHP

 0; \$i--)    {        // Check if arr[i]        // is not in order        if (\$arr[\$i] < \$arr[\$i - 1])        {            // Find the other element            // to be swapped with arr[i]            \$j = \$i - 1;            while (\$j >= 0 && \$arr[\$i] < \$arr[\$j])                \$j--;             // Swap the pair            \$temp = \$arr[\$i];            \$arr[\$i] = \$arr[\$j + 1];            \$arr[\$j + 1] = \$temp;                 break;        }    }} // A utility function to// print an array of size nfunction printArray(&\$arr, \$n){    for (\$i = 0; \$i < \$n; \$i++)        echo \$arr[\$i] . " ";    echo "\n";} // Driver Code\$arr = array(10, 30, 20,        40, 50, 60, 70);\$n = sizeof(\$arr); echo "Given array is " . "\n";printArray(\$arr, \$n); sortByOneSwap(\$arr, \$n); echo "Sorted array is ". "\n";printArray(\$arr, \$n); // This code is contributed by Akanksha Rai

## Javascript



Output :

Given array is
10 30 20 40 50 60 70
Sorted array is
10 20 30 40 50 60 70

Time Complexity: O(N), as we are using a loop to traverse the array.

Auxiliary Space: O(1), as we are not using extra space.
The above program works in O(n) time and swaps only one element.