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Python3 Program to Find the Mth element of the Array after K left rotations

Given non-negative integers K, M, and an array arr[] with N elements find the Mth element of the array after K left rotations.

Examples:

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}
1st element after 2 left rotations is 5.

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

Naive Approach: The idea is to Perform Left rotation operation K times and then find the Mth element of the final array.

Time Complexity: O(N * K)
Auxiliary Space: 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.

3.
Below is the implementation of the above approach:

Python3

 `# Python3 program for the above approach `` ` `# Function to return Mth element of ``# array after k left rotations ``def` `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 ``    ``index ``=` `(K ``+` `M ``-` `1``) ``%` `N `` ` `    ``result ``=` `a[index] `` ` `    ``# Return the result ``    ``return` `result `` ` `# Driver Code ``if` `__name__ ``=``=` `'__main__'``: ``     ` `    ``# Array initialization ``    ``a ``=` `[ ``3``, ``4``, ``5``, ``23` `] `` ` `    ``# Size of the array ``    ``N ``=` `len``(a) `` ` `    ``# Given K rotation and Mth element ``    ``# to be found after K rotation ``    ``K ``=` `2``    ``M ``=` `1`` ` `    ``# Function call ``    ``print``(getFirstElement(a, N, K, M)) `` ` `# This code is contributed by mohit kumar 29 `

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!

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