Sort an almost sorted array where only two elements are swapped

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Sort an almost sorted array where only two elements are swapped

Vinay Khatri
Last updated on September 21, 2022

    Problem

    How can an almost-sorted array with only two members swapped be effectively sorted?

    Sample Input

    [1, 5, 3]

    Sample Output

    [1, 3, 5]

    Explanation

    3 and 5 got swapped

    Approach

    The goal is to go from right to left and discover the first out-of-order number (a number that is smaller than the previous number). Once the first number is located, traverse the array toward the left side to find the other out-of-order element. The approach takes O(N) time.

    C++ Programming

    #include<iostream>
    #include<algorithm>
    using namespace std;
    
    //function to sort an array
    void sortArray(int arr[], int n)
    {
        // Traverse the given array from right side
        for (int i = n-1; i > 0; i--)
        {
            // if arr[i] is not in order
            if (arr[i] < arr[i-1])
            {
                int j = i-1;
                while (j>=0 && arr[i] < arr[j])
                    j--;
                swap(arr[i], arr[j+1]);
                break;
            }
        }
    }
    int main()
    {
        int arr[] = {1, 5, 3};
        int n = sizeof(arr)/sizeof(arr[0]);
    
    
        sortArray(arr, n);
    
        for(int i=0;i<n;i++) cout<<arr[i]<<" ";
        return 0;
    }
    

    Output

    1 3 5

    C Programming

    #include<stdio.h>
    
    //function to sort an array
    void sortArray(int arr[], int n)
    {
        // Traverse the given array from right side
        for (int i = n-1; i > 0; i--)
        {
            // if arr[i] is not in order
            if (arr[i] < arr[i-1])
            {
                int j = i-1;
                while (j>=0 && arr[i] < arr[j])
                    j--;
                int temp = arr[i];  //swap the elements
                arr[i] = arr[j+1];
                arr[j+1] = temp;
                break;
            }
        }
    }
    void main()
    {
        int arr[] = {1, 5, 3};
        int n = sizeof(arr)/sizeof(arr[0]);
    
        sortArray(arr, n);
        for(int i=0;i<n;i++) printf("%d ",arr[i]);
    }

    Output

    1 3 5

    Java Programming

    import java.io.*;
    
    class Solution
    {
    //function to sort 
    static void sortArray(int arr[], int n)
    {
       // Traverse the given array
       // from right side
       for (int i = n - 1; i > 0; i--)
       {
         // 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 
          int temp = arr[i];
          arr[i] = arr[j + 1];
          arr[j + 1] = temp;
         
          break;
         }
       }
    }
    
    public static void main(String[] args)
    {
       int arr[] = {1, 5, 3};
       int n = arr.length;
       
       sortArray(arr, n);
    
       for (int i = 0; i < n; i++)
          System.out.print(arr[i] + " ");
        System.out.println();
    }
    }

    Output

    1 3 5

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    Tags:
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