Movement Algorithms

Shuffling a Partial Range

Can you use std::ranges::shuffle() with a partial range of a container, and how?

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Yes, you can use std::ranges::shuffle() with a partial range of a container. This is useful when you want to randomize only a specific portion of a container while leaving the rest intact.

Using std::ranges::shuffle() with a Partial Range

To shuffle a partial range, you can provide iterators that define the subrange you want to shuffle. Here’s an example:

#include <algorithm>
#include <iostream>
#include <random>
#include <vector>

int main() {
  std::vector<int> data{1, 2, 3, 4, 5, 6, 7, 8};

  std::random_device rd;
  std::mt19937 gen(rd());

  // Shuffle only the first 5 elements
  std::ranges::shuffle(data.begin(),
    data.begin() + 5, gen);

  for (const auto& value : data) {
    std::cout << value << " ";
  }
}
4 1 3 5 2 6 7 8

Step-by-Step Guide

  1. Define the Range: Identify the portion of the container you want to shuffle. Use iterators to specify the start and end of this subrange.
  2. Provide a Random Number Generator (RNG): std::ranges::shuffle() requires an RNG. Here, we use std::mt19937 from the <random> header.
  3. Call the std::ranges::shuffle algorithm: Pass the iterators for the subrange and the RNG to std::ranges::shuffle().

Practical Example

Consider a scenario where you want to shuffle only the middle part of a vector:

#include <algorithm>
#include <iostream>
#include <random>
#include <vector>

int main() {
  std::vector<int> numbers{
    10, 20, 30, 40, 50, 60, 70, 80, 90, 100};

  std::random_device rd;
  std::mt19937 gen(rd());

  // Shuffle elements from index 3 to 7
  std::ranges::shuffle(
    numbers.begin() + 3,
    numbers.begin() + 8,
    gen
  );

  for (const auto& num : numbers) {
    std::cout << num << " ";
  }
}
10 20 30 80 70 60 40 50 90 100

Considerations

  • Range Boundaries: Ensure that the iterators provided do not exceed the container’s boundaries to avoid undefined behavior.
  • Random Device: Using std::random_device for seeding the RNG ensures better randomness compared to a fixed seed.

Conclusion

Using std::ranges::shuffle() with a partial range of a container is straightforward.

By specifying the appropriate iterators, you can shuffle any subrange within your container, giving you flexibility in how you randomize elements.

This approach is particularly useful in scenarios where only a segment of data needs to be randomized.

Answers to questions are automatically generated and may not have been reviewed.

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