Программа Javascript для поиска M-го элемента массива после K левых поворотов

Даны неотрицательные целые числа K , M и массив arr[] с N элементами, найдите M ^-й элемент массива после K левых поворотов.

Примеры:

Input: arr[] = {3, 4, 5, 23}, K = 2, M = 1
Output: 5
Explanation: 
The array after first left rotation a₁[ ] = {4, 5, 23, 3}
The array after second left rotation a₂[ ] = {5, 23, 3, 4}
st element after 2 left rotations is 5.

Input: arr[] = {1, 2, 3, 4, 5}, K = 3, M = 2
Output: 5 
Explanation: 
The array after 3 left rotation has 5 at its second position.

Наивный подход: идея состоит в том, чтобы выполнить операцию поворота влево K раз, а затем найти M ^-й элемент конечного массива.

Временная сложность: O(N * K)
Вспомогательное пространство: O(N)

Efficient Approach: To optimize the problem, observe the following points:

1. If the array is rotated N times it returns the initial array again.
   

   For example, a[ ] = {1, 2, 3, 4, 5}, K=5 then the array after 5 left rotation a₅[ ] = {1, 2, 3, 4, 5}.

   Therefore, the elements in the array after Kth rotation is the same as the element at index K%N in the original array.

2. The Mth element of the array after K left rotations is
   

   { (K + M – 1) % N }th

   element in the original array.

 
Below is the implementation of the above approach:

Javascript








<script>    // Javascript program for the above approach         // Function to return Mth element of     // array after k left rotations     function getFirstElement(a , N , K , M) {            // The array comes to original state         // after N rotations         K %= N;            // Mth element after k left rotations         // is (K+M-1)%N th element of the         // original array         var index = (K + M - 1) % N;            var result = a[index];            // Return the result         return result;     }        // Driver code                   // Array initialization         var a = [ 3, 4, 5, 23 ];            // Size of the array         var N = a.length;            // Given K rotation and Mth element         // to be found after K rotation         var K = 2, M = 1;            // Function call         document.write(getFirstElement(a, N, K, M));    // This code contributed by gauravrajput1     </script>

Output: 

5

 

Time complexity: O(1)
Auxiliary Space: O(1)

Please refer complete article on Find the Mth element of the Array after K left rotations for more details!