find_all_constexpr

find_all_constexpr.cpp

#include <array>
#include <algorithm>
#include <string_view>
#include <utility>
#include <iostream>
#include <cstdint>


// Helper to get the first character of a string_view
consteval uint8_t get_first_char(std::string_view sv) {
    if(sv.empty()) { return 0; }
    return sv[0];
}

// Helper to find the range of strings starting with a given character
template<size_t N>
consteval std::pair<int, int> find_char_range(std::array<std::string_view, N>&arr, uint8_t c) {
    auto it = std::lower_bound(arr.data(), arr.data() + N, c, 
        [](const auto& sv, char ch) { return get_first_char(sv) < ch; });
    if (it == arr.data() + N || get_first_char(*it) != c) return {-1, -1};
    
    auto end = std::upper_bound(it, arr.data() + N, c, 
        [](char ch, const auto& sv) { return ch < get_first_char(sv); });
    
    return {static_cast<int>(it - arr.data()), static_cast<int>(end - arr.data() - 1)};
}

// Main function to sort and find ranges
template<size_t N>
consteval std::pair<std::array<std::pair<int, int>, 256>,std::array<std::string_view, N>> sort_and_range(const std::array<std::string_view, N>& arr) {
    // Create a copy of the array to sort
    std::array<std::string_view, N> sorted_arr = arr;
    std::sort(sorted_arr.begin(), sorted_arr.end(), 
        [](const auto& a, const auto& b) { return get_first_char(a) < get_first_char(b); });

    // Find ranges for each character
    std::array<std::pair<int, int>, 256> result = {std::make_pair(-1, -1)};
    for (int c = 0; c < 256; ++c) {
        result[c] = find_char_range(sorted_arr, c);
    }
    return {result, sorted_arr};
}


bool ping(std::string_view v) {
    static constexpr std::array<std::string_view, 5> otest_array = {
        "banana", "apple", "cherry", "date", "elderberry"
    };

    static constexpr auto c = sort_and_range(otest_array);
    static constexpr auto result = c.first;
    static constexpr auto test_array = c.second;
    auto [start, end] = result[uint8_t(v[0])];
    if(start == -1) { return false; }
    for(int s = start; s <= end; s++) {
        if(v == test_array[s]) { return true; }
    } 
    return false;
}

bool get(std::string_view x) {
    return ping(x);
}