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985c397 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 | /// The MIT License (MIT)
/// Copyright (c) 2016 Peter Goldsborough
///
/// Permission is hereby granted, free of charge, to any person obtaining a copy
/// of this software and associated documentation files (the "Software"), to
/// deal in the Software without restriction, including without limitation the
/// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
/// sell copies of the Software, and to permit persons to whom the Software is
/// furnished to do so, subject to the following conditions:
///
/// The above copyright notice and this permission notice shall be included in
/// all copies or substantial portions of the Software.
///
/// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
/// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
/// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
/// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
/// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
/// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
/// IN THE SOFTWARE.
#include <iostream>
#include "lru/lru.hpp"
using Cache = LRU::Cache<int, int>;
int fibonacci(int n, Cache& cache) {
if (n < 2) return 1;
// We internally keep track of the last accessed key, meaning a
// `contains(key)` + `lookup(key)` sequence will involve only a single hash
// table lookup.
if (cache.contains(n)) return cache[n];
auto value = fibonacci(n - 1, cache) + fibonacci(n - 2, cache);
// Caches are 100% move-aware and we have implemented
// `unordered_map` style emplacement and insertion.
cache.emplace(n, value);
return value;
}
int fibonacci(int n) {
// Use a capacity of 100 (after 100 insertions, the next insertion will evict
// the least-recently accessed element). The default capacity is 128. Note
// that for fibonacci, a capacity of 2 is sufficient (and ideal).
Cache cache(100);
return fibonacci(n, cache);
}
auto main() -> int {
std::cout << fibonacci(32) << std::endl;
}
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