AdventOfCode2020/ndarray.h at master · ashermkn1/AdventOfCode2020 · GitHub

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#pragma once

#include <numeric>
#include <vector>

template<typename T>
T product(const std::vector<T>& numbers) {
    return std::accumulate(numbers.cbegin(), numbers.cend(), (T) 1, std::multiplies<T>());
}

using index_item_t = int64_t;
using index_t = std::vector<index_item_t>;

/**
 * multidimensional array
 * @tparam T element type
 */
template<typename T>
class NDArray {
public:
    // constructors
    explicit NDArray(const std::vector<size_t>& shape);

    NDArray(const std::vector<size_t>& shape, const index_t& offsets);

    NDArray(const std::vector<size_t>& shape, const index_t& offsets, const std::vector<T>& data);
    // access data
    [[nodiscard]]
    auto& at(const index_t& index) {
        if (!isValidIndex(index)) {
            throw std::runtime_error("Invalid index.");
        }
        size_t internal = 0;
        for (size_t i = 0; i < _shape.size(); i++) {
            internal += size_t((index[i] - _offsets[i]) * _strides[i]);
        }
        return _data.at(internal);
    }

    [[nodiscard]]
    const auto& at(const index_t& index) const {
        if (!isValidIndex(index)) {
            throw std::runtime_error("Invalid index.");
        }
        size_t internal = 0;
        for (size_t i = 0; i < _shape.size(); i++) {
            internal += size_t((index[i] - _offsets[i]) * _strides[i]);
        }
        return _data.at(internal);
    }
    // set data
    void set(const index_t& index, const T& value) {
        if (!isValidIndex(index)) {
            throw std::runtime_error("Invalid index.");
        }
        size_t internal = 0;
        for (size_t i = 0; i < _shape.size(); i++) {
            internal += size_t((index[i] - _offsets[i]) * _strides[i]);
        }
        _data[internal] = value;
    }

    [[nodiscard]]
    bool isValidIndex(const index_t& index) const {
        for (size_t i = 0; i < _shape.size(); i++) {
            if ((index[i] < _offsets[i]) || (index[i] >= _shape[i] + _offsets[i])) {
                return false;
            }
        }
        return true;
    }
    // getters
    [[nodiscard]]
    const std::vector<size_t>& shape() const {
        return _shape;
    }

    [[nodiscard]]
    const index_t& offsets() const {
        return _offsets;
    }
    // total amount of elements in array
    [[nodiscard]]
    size_t size() const {
        return product(_shape);
    }
    // number of dimensions
    [[nodiscard]]
    size_t ndim() const {
        return _shape.size();
    }
    // sum of all elements
    [[nodiscard]]
    T sum() const {
        return std::accumulate(_data.cbegin(), _data.cend(), 0, std::plus<T>());
    }

    NDArray<T>& operator=(const T& val) {
        _data = std::vector(size(), val);
    }
private:
    std::vector<T> _data;

    std::vector<size_t> _shape;

    std::vector<size_t> _strides;

    index_t _offsets;

    void _calculateStrides();
};

template<typename T>
NDArray<T>::NDArray(const std::vector<size_t>& shape): _shape(shape),
                    _data(product(shape)), _offsets(shape.size(), 0) {
    _calculateStrides();
}

template<typename T>
NDArray<T>::NDArray(const std::vector<size_t>& shape, const index_t& offsets) {
    if (offsets.size() != shape.size()) {
        throw std::runtime_error("Invalid offset size.");
    }
    _shape = shape;
    _offsets = offsets;
    _data = std::vector<T>(product(shape));
    _calculateStrides();
}

template<typename T>
NDArray<T>::NDArray(const std::vector<size_t>& shape, const index_t& offsets, const std::vector<T>& data) {
    if (data.size() != product(shape)) {
        throw std::runtime_error("Invalid shape.");
    }
    if (shape.size() != offsets.size()) {
        throw std::runtime_error("Invalid offsets.");
    }
    _shape = shape;
    _data = data;
    _offsets = offsets;
    _calculateStrides();
}

template<typename T>
void NDArray<T>::_calculateStrides() {
    _strides = std::vector<size_t>(ndim());
    (*_strides.rbegin()) = 1;

    if (ndim() == 1) {
        return;
    }
    for (int i = _strides.size() - 1; i >= 0; i--) {
        _strides[i] = _strides[i + 1] * _shape[i + 1];
    }
}