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feat: add lru caching algorithm (#1557)

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* updating DIRECTORY.md

* feat: add lru caching algorithm

* removing clang tidy warnings

* updating DIRECTORY.md

* clang-format and clang-tidy fixes for fcb50fb7

* docs updated

* clang-format and clang-tidy fixes for ee18e3aa

* using list instead of bits/stdc++.h

* clang-format and clang-tidy fixes for 19d09e85

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* clang-format and clang-tidy fixes for 4e223bc3

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* clang-format and clang-tidy fixes for 4bea23ef

* using uint for non negative numbers

* clang-format and clang-tidy fixes for 87e7df55

* Update others/lru_cache.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* clang-format and clang-tidy fixes for b423fd4b

* suggestions applied

* clang-format and clang-tidy fixes for e3ba29eb

* Update others/lru_cache.cpp

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Co-authored-by: David Leal <halfpacho@gmail.com>
Co-authored-by: Abhinn Mishra <49574460+mishraabhinn@users.noreply.github.com>
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1
DIRECTORY.md
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@ -242,6 +242,7 @@
* [Fast Integer Input](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/others/fast_integer_input.cpp)
* [Happy Number](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/others/happy_number.cpp)
* [Iterative Tree Traversals](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/others/iterative_tree_traversals.cpp)
* [Lru Cache](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/others/lru_cache.cpp)
* [Matrix Exponentiation](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/others/matrix_exponentiation.cpp)
* [Palindrome Of Number](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/others/palindrome_of_number.cpp)
* [Paranthesis Matching](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/others/paranthesis_matching.cpp)

3
hashing/chaining.cpp
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@ -164,7 +164,8 @@ int main() {
case 3:
std::cout << "Enter element to generate hash = " << std::endl;
std::cin >> x;
std::cout << "Hash of " << x << " is = " << mychain.hash(x) << std::endl;
std::cout << "Hash of " << x << " is = " << mychain.hash(x)
<< std::endl;
break;
case 4:
mychain.display();

268
others/lru_cache.cpp Normal file
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@ -0,0 +1,268 @@
/**
* @file
* @brief An implementation of
* [LRU
* Cache](https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)).
* Lru is a part of cache algorithms (also frequently called cache replacement
* algorithms or cache replacement policies).
*
* ### Logic
* * Discards the least recently used items first.
* * This algorithm requires keeping track of what was used when, which is
* expensive if one wants to make sure the algorithm always discards the least
* recently used item.
* * General implementations of this technique require keeping "age bits"
* for cache-lines and track the "Least Recently Used" cache-line based on
* age-bits.
* * In such an implementation, every time a cache-line is used, the age of
* all other cache-lines changes
*
* ### Algorithm explanation
* For a cache of page frame x:
* * Check if the page is present in cache.
* * If not present, then check is the cache is full or not:
* * If the cache is full, REMOVE the last element from the cache.
* * If the element is present in cache, then shift that element to
* first position in cache from its original position.
* * This way you can keep the least recently used elements in the
* last and most recently used in front of the cache.
*
* Every time a requested page is not found in cache, that is a miss or page
* fault, and if the page is present in cache, then its a hit.
*
* ## Data Structure used
* * In the algorithm below we used two different data structure, one is linked
* list and other one is a hash map
* * The linked list is used to contain the pages and the hash map contains the
* pages and their address.
* * Every time a new page is requested, we first check in the hash map if the
* page is present or not.
* * If not present, and the cache is full, we simply delete the last entry in
* the cache.
* * If present, we shift that page from its current location to beginning of
* the cache and update the address in hash map for that page.
*
* @author [Nitin Sharma](https://github.com/foo290)
* */
#include <cassert> /// for assert
#include <iostream> /// for IO Operations
#include <list> /// for std::list
#include <unordered_map> /// for std::unordered_map
/**
* @namespace others
* @brief Other algorithms
*/
namespace others {
/**
* @namespace lru_cache
* @brief Implementation of the [LRU caching
* algorithm](https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU))
*/
namespace lru_cache {
/**
* @brief LRU cache class
*/
class LRUCache {
uint64_t pageFrame; ///< Page frame, or total size of the cache.
std::list<uint64_t> cache; ///< Cache linked list (using the STL)
std::unordered_map<uint64_t, std::list<uint64_t>::iterator>
pageMap; ///< Hash map containing pages and their addresses
uint64_t hits =
0; ///< Total number of hits, or total number of times a page
///< was found in cache.
uint64_t pageFault = 0; ///< Total number of miss/page fault, or total
///< number of times a page was not found in cache
public:
/**
* @brief Constructor, Initialize thee LRU class with page frame.
* @param pf Page frame or total size of cache.
* */
explicit LRUCache(uint64_t pf) { pageFrame = pf; }
/**
* @brief Refer to a page, or request a page from memory.
* @param page The page that you are referring to.
* @returns void
* */
void refer(uint64_t page) {
// If the page requested not in cache.
if (pageMap.find(page) == pageMap.end()) {
pageFault++; ///< Increase the page fault by one.
// Check if the cache is full
if (cache.size() == pageFrame) {
// delete the last page from cache
uint64_t lastPage = cache.back();
cache.pop_back();
pageMap.erase(lastPage);
}
}
// The requested page is in the cache
else {
hits++;
// present in cache, erase from current position to bring in front
cache.erase(pageMap[page]);
}
// Push it in the front of the cache and update the page reference in
// page map.
cache.push_front(page);
pageMap[page] = cache.begin();
}
/**
* @brief A function to display the current cache
* @returns Void
* */
void display() {
for (uint64_t &it : cache) {
std::cout << it << " ";
}
std::cout << std::endl;
}
/**
* @brief A function to get page hits
* @returns int
* */
uint64_t getHits() const { return hits; }
/**
* @brief A function to get page fault
* @returns int
* */
uint64_t getPageFault() const { return pageFault; }
};
} // namespace lru_cache
} // namespace others
namespace lru_tests {
/**
* @brief A function to print given message on console.
* @tparam T Type of the given message.
* @returns void
* */
template <typename T>
void log(T msg) {
// It's just to avoid writing cout and endl
std::cout << "[TESTS] : ---> " << msg << std::endl;
}
/**
* @brief A simple test case
* The assert statement will check expected hist and miss to resultant hits and
* miss
* @returns void
* */
static void test_1() {
uint64_t expected_hits = 2;
uint64_t expected_pageFault = 4;
log("Running Test-1...");
others::lru_cache::LRUCache cache(4);
cache.refer(1);
cache.refer(2);
cache.refer(5);
cache.refer(1);
cache.refer(4);
cache.refer(5);
log("Checking assert statement...");
assert(cache.getHits() == expected_hits &&
cache.getPageFault() == expected_pageFault);
log("Assert successful!");
log("Test-1 complete!");
}
/**
* @brief A test case contains hits more than cache size
* The assert statement will check expected hist and miss to resultant hits and
* miss
* @returns void
* */
static void test_2() {
uint64_t expected_hits = 4;
uint64_t expected_pageFault = 2;
log("Running Test-2...");
others::lru_cache::LRUCache cache(4);
cache.refer(1);
cache.refer(1);
cache.refer(1);
cache.refer(1);
cache.refer(1);
cache.refer(5);
log("Checking assert statement...");
assert(cache.getHits() == expected_hits &&
cache.getPageFault() == expected_pageFault);
log("Assert successful!");
log("Test-2 complete!");
}
/**
* @brief A simple test case
* The assert statement will check expected hist and miss to resultant hits and
* miss
* @returns void
* */
static void test_3() {
uint64_t expected_hits = 1;
uint64_t expected_pageFault = 5;
log("Running Test-3...");
others::lru_cache::LRUCache cache(4);
cache.refer(1);
cache.refer(2);
cache.refer(3);
cache.refer(4);
cache.refer(5);
cache.refer(5);
log("Checking assert statement...");
assert(cache.getHits() == expected_hits &&
cache.getPageFault() == expected_pageFault);
log("Assert successful!");
log("Test-3 complete!");
}
/**
* @brief A function to invoke all test cases
* @returns void
* */
static void run_tests() {
test_1();
test_2();
test_3();
log("");
log("TESTS COMPLETED!");
}
} // namespace lru_tests
/**
* @brief Main function
* @returns 0 on exit
*/
int main() {
lru_tests::run_tests();
// Usage
others::lru_cache::LRUCache cache(4);
cache.refer(1);
cache.refer(2);
cache.refer(3);
cache.refer(4);
cache.refer(5);
cache.refer(5);
cache.display();
std::cout << "Hits: " << cache.getHits()
<< " Miss: " << cache.getPageFault() << std::endl;
return 0;
}