Check if two arrays can be made equal by reversing any subarray once

Last Updated : 17 Aug, 2021

Given two arrays A[] and B[] of equal size N, the task is to check whether A[] can be made equal to B[] by reversing any sub-array of A only once.

Examples:

Input: A[] = {1, 3, 2, 4}
B[] = {1, 2, 3, 4}
Output: Yes
Explanation:
The sub-array {3, 2} can be reversed to {2, 3}, which makes A equal to B.

Input: A[] = {1, 4, 2, 3}
B[] = {1, 2, 3, 4}
Output: No
Explanation:
There is no sub-array of A which, when reversed, makes A equal to B.

Naive Approach: Check for all sub-arrays of A[] and compare the two arrays after reversing the sub-array.
Time complexity: O(N²).

Efficient Approach:

First, find the starting and the ending index of the sub-array not equal in A and B.
Then, by reversing the required sub-array, we can check whether A can be made equal to B or not.
The starting index is the first index in the arrays for which A[i] != B[i] and the ending index is the last index in arrays for which A[i] != B[i].

Below is the implementation of the above approach.

C++

   // C++ implementation to
// check whether two arrays
// can be made equal by
// reversing a sub-array
// only once
#include <bits/stdc++.h>
using namespace std;
 
// Function to check whether two arrays
// can be made equal by reversing
// a sub-array only once
void checkArray(int A[], int B[], int N)
{
    // Integer variable for
    // storing the required
    // starting and ending
    // indices in the array
    int start = 0;
    int end = N - 1;
 
    // Finding the smallest index
    // for which A[i] != B[i]
    // i.e the starting index
    // of the unequal sub-array
    for (int i = 0; i < N; i++) {
        if (A[i] != B[i]) {
            start = i;
            break;
        }
    }
    // Finding the largest index
    // for which A[i] != B[i]
    // i.e the ending index
    // of the unequal sub-array
    for (int i = N - 1; i >= 0; i--) {
        if (A[i] != B[i]) {
            end = i;
            break;
        }
    }
 
    // Reversing the sub-array
    // A[start], A[start+1] .. A[end]
    reverse(A + start, A + end + 1);
 
    // Checking whether on reversing
    // the sub-array A[start]...A[end]
    // makes the arrays equal
 
    for (int i = 0; i < N; i++) {
        if (A[i] != B[i]) {
            // If any element of the
            // two arrays is unequal
            // print No and return
            cout << "No" << endl;
            return;
        }
    }
    // Print Yes if arrays are
    // equal after reversing
    // the sub-array
    cout << "Yes" << endl;
}
// Driver code
int main()
{
    int A[] = { 1, 3, 2, 4 };
    int B[] = { 1, 2, 3, 4 };
    int N = sizeof(A) / sizeof(A[0]);
    checkArray(A, B, N);
 
    return 0;
}
 
  

Java

   // Java implementation to
// check whether two arrays
// can be made equal by
// reversing a sub-array
// only once
import java.util.*; 
class GFG{
  
// Function to check whether two arrays
// can be made equal by reversing
// a sub-array only once
static void checkArray(int A[], int B[], int N)
{
    // Integer variable for
    // storing the required
    // starting and ending
    // indices in the array
    int start = 0;
    int end = N - 1;
  
    // Finding the smallest index
    // for which A[i] != B[i]
    // i.e the starting index
    // of the unequal sub-array
    for (int i = 0; i < N; i++) 
    {
        if (A[i] != B[i]) 
        {
            start = i;
            break;
        }
    }
    // Finding the largest index
    // for which A[i] != B[i]
    // i.e the ending index
    // of the unequal sub-array
    for (int i = N - 1; i >= 0; i--)
    {
        if (A[i] != B[i])
        {
            end = i;
            break;
        }
    }
  
    // Reversing the sub-array
    // A[start], A[start+1] .. A[end]
    Collections.reverse(Arrays.asList(A)); 
  
    // Checking whether on reversing
    // the sub-array A[start]...A[end]
    // makes the arrays equal
    for (int i = 0; i < N; i++) 
    {
        if (A[i] != B[i])
        {
            // If any element of the
            // two arrays is unequal
            // print No and return
            System.out.println("No");
            return;
        }
    }
    // Print Yes if arrays are
    // equal after reversing
    // the sub-array
   System.out.println("Yes");
}
// Driver code
public static void main(String[] args) 
{
    int A[] = { 1, 3, 2, 4 };
    int B[] = { 1, 2, 3, 4 };
    int N = A.length;
    checkArray(A, B, N);
}
}
 
// This Code is contributed by rock_cool
 
  

Python3

   # Python3 implementation to
# check whether two arrays
# can be made equal by
# reversing a sub-array
# only once
 
# Function to check whether two arrays
# can be made equal by reversing
# a sub-array only once
def checkArray(A, B, N):
     
    # Integer variable for
    # storing the required
    # starting and ending
    # indices in the array
    start = 0
    end = N - 1
 
    # Finding the smallest index
    # for which A[i] != B[i]
    # i.e the starting index
    # of the unequal sub-array
    for i in range(N):
        if (A[i] != B[i]):
            start = i
            break
             
    # Finding the largest index
    # for which A[i] != B[i]
    # i.e the ending index
    # of the unequal sub-array
    for i in range(N - 1, -1, -1):
        if (A[i] != B[i]):
            end = i
            break
 
    # Reversing the sub-array
    # A[start], A[start+1] .. A[end]
    A[start:end + 1] = reversed(A[start:end + 1])
     
    # Checking whether on reversing
    # the sub-array A[start]...A[end]
    # makes the arrays equal
    for i in range(N):
        if (A[i] != B[i]):
             
            # If any element of the
            # two arrays is unequal
            # print No and return
            print("No")
            return
             
    # Print Yes if arrays are
    # equal after reversing
    # the sub-array
    print("Yes")
     
# Driver code
if __name__ == '__main__':
     
    A = [ 1, 3, 2, 4 ]
    B = [ 1, 2, 3, 4 ]
    N = len(A)
     
    checkArray(A, B, N)
     
# This code is contributed by mohit kumar 29
 
  

C#

   // C# implementation to
// check whether two arrays
// can be made equal by
// reversing a sub-array
// only once
using System;
 
class GFG{
 
// Function to check whether two arrays
// can be made equal by reversing
// a sub-array only once
static void checkArray(int []A, int []B, int N)
{
     
    // Integer variable for
    // storing the required
    // starting and ending
    // indices in the array
    int start = 0;
    int end = N - 1;
 
    // Finding the smallest index
    // for which A[i] != B[i]
    // i.e the starting index
    // of the unequal sub-array
    for(int i = 0; i < N; i++) 
    {
        if (A[i] != B[i]) 
        {
            start = i;
            break;
        }
    }
     
    // Finding the largest index
    // for which A[i] != B[i]
    // i.e the ending index
    // of the unequal sub-array
    for(int i = N - 1; i >= 0; i--)
    {
        if (A[i] != B[i])
        {
            end = i;
            break;
        }
    }
 
    // Reversing the sub-array
    // A[start], A[start+1] .. A[end]
    Array.Reverse(A, start, end);
 
 
    // Checking whether on reversing
    // the sub-array A[start]...A[end]
    // makes the arrays equal
    for(int i = 0; i < N; i++) 
    {
        if (A[i] != B[i])
        {
             
            // If any element of the
            // two arrays is unequal
            // print No and return
            Console.Write("No");
            return;
        }
    }
     
    // Print Yes if arrays are
    // equal after reversing
    // the sub-array
    Console.Write("Yes");
}
 
// Driver code
public static void Main(string[] args) 
{
    int []A = { 1, 3, 2, 4 };
    int []B = { 1, 2, 3, 4 };
    int N = A.Length;
    checkArray(A, B, N);
}
}
 
// This code is contributed by rutvik_56
 
  

Javascript

   <script>
 
 
// Javascript implementation to
// check whether two arrays
// can be made equal by
// reversing a sub-array
// only once
 
// Function to check whether two arrays
// can be made equal by reversing
// a sub-array only once
function checkArray(A, B, N)
{
    // Integer variable for
    // storing the required
    // starting and ending
    // indices in the array
    var start = 0;
    var end = N - 1;
 
    // Finding the smallest index
    // for which A[i] != B[i]
    // i.e the starting index
    // of the unequal sub-array
    for (var i = 0; i < N; i++) {
        if (A[i] != B[i]) {
            start = i;
            break;
        }
    }
    // Finding the largest index
    // for which A[i] != B[i]
    // i.e the ending index
    // of the unequal sub-array
    for (var i = N - 1; i >= 0; i--) {
        if (A[i] != B[i]) {
            end = i;
            break;
        }
    }
 
    // Reversing the sub-array
    // A[start], A[start+1] .. A[end]
    var l = start;
    var r = end;
    var d = parseInt((r-l+2)/2);
      for(var i=0;i<d;i++)
      {
         var t = A[l+i];
         A[l+i] = A[r-i];
         A[r-i] = t;
      }
 
    // Checking whether on reversing
    // the sub-array A[start]...A[end]
    // makes the arrays equal
 
    for (var i = 0; i < N; i++) {
        if (A[i] != B[i]) {
            // If any element of the
            // two arrays is unequal
            // print No and return
            document.write( "No" );
            return;
        }
    }
    // Print Yes if arrays are
    // equal after reversing
    // the sub-array
    document.write( "Yes" );
}
// Driver code
var A = [1, 3, 2, 4];
var B = [1, 2, 3, 4];
var N = A.length;
checkArray(A, B, N);
 
 
</script>
 
  

Output:

Yes

Time Complexity: O(N)
Auxiliary Space: O(1)

Check if Arrays can be made equal by Replacing elements with their number of Digits

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Check if two arrays can be made equal by reversing any subarray once

C++

Java

Python3

C#

Javascript

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