Rotate Array

Rotating an array to the right by k steps can be achieved in a few ways. One simple method is to reverse parts of the array to get the final rotated array. Here’s a step-by-step guide:

Handle Multiple Rotations: If k is greater than the length of the array, you only need to rotate k % len(nums) steps.
Reverse the Entire Array: First, reverse the entire array.
Reverse the First k Elements: Then, reverse the first k elements.
Reverse the Remaining Elements: Finally, reverse the remaining len(nums) - k elements.

These steps will rotate the array to the right by k steps without using extra space.

Here’s the code:

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class Solution:
    def rotate(self, nums: List[int], k: int) -> None:
        k %= len(nums)

        def reverse(start: int, end: int):
            while start < end:
                nums[start], nums[end] = nums[end], nums[start]
                start += 1
                end -= 1

        # Reverse the entire array
        reverse(0, len(nums) - 1)

        # Reverse the first k elements
        reverse(0, k - 1)

        # Reverse the remaining elements
        reverse(k, len(nums) - 1)

Explanation:

By performing these reversals, you effectively rotate the array to the right by k steps.
The reverse function is used to reverse the elements in the range [start, end].
This solution modifies the array in place without using extra space, and it meets the problem’s constraints.

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class Solution:
    def rotate(self, nums: List[int], k: int) -> None:
        n=len(nums)
        k=k%n
        nums[:n-k]=nums[:n-k][::-1]
        nums[n-k:]=nums[n-k:][::-1]
        nums[:]=nums[::-1]

Problem Classification

Language Agnostic Coding Drills

Basic Syntax and Structure: Understand how to declare a function, define parameters, and write function bodies.
Basic Data Types: Understand what are integers, lists, and strings, and how to use them.
Variables and Assignment: Learn how to assign values to variables, and how to update their values.
List Indexing: Learn how to access individual elements in a list using indices.
Slicing: Understand how to slice lists to access a subset of the elements.
List Methods: Understand built-in list methods like len() to find the length of a list.
Arithmetic Operations: Understand basic arithmetic operations like modulus (%).
Class Structure: Learn how to create a class and define methods within a class.
Slice Assignment: Understand how to assign a new list to a slice of an existing list.
List Reversing: Understand how to reverse a list or a slice of a list using [::-1].

These concepts, when understood and practiced separately, can be combined to understand and implement the provided code.

Targeted Drills in Python

Basic Syntax and Structure:

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# Define a function called greet that prints "Hello, World!".
def greet():
    pass  # Your code here

Basic Data Types:

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# Declare an integer variable named "my_int" with value 10, a list variable named "my_list" with values 1, 2, 3 and a string variable named "my_str" with value "Hello".

Variables and Assignment:

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# Declare a variable "a" with value 5, then assign the value 10 to "a".

List Indexing:

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# Given the list "numbers" below, print the second element of the list.
numbers = [5, 8, 2, 4, 7, 10]

Slicing:

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# Given the list "numbers", print the sublist containing the second to fourth elements (inclusive).
numbers = [5, 8, 2, 4, 7, 10]

List Methods:

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# Given the list "numbers", print the length of the list.
numbers = [5, 8, 2, 4, 7, 10]

Arithmetic Operations:

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# Calculate the modulus of 10 and 3, and print the result.

Class Structure:

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# Define a class called "MyClass" with a method called "my_method" that prints "This is my method.".

Slice Assignment:

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# Given the list "numbers" below, replace the second and third elements with 20 and 30, respectively.
numbers = [5, 8, 2, 4, 7, 10]

List Reversing:

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# Given the list "numbers" below, create a new list that is the reverse of "numbers".
numbers = [5, 8, 2, 4, 7, 10]