Skip to content

Commit

Permalink
fix: add cstdint to gale shapely
Browse files Browse the repository at this point in the history
  • Loading branch information
@realstealthninja
realstealthninja committed Oct 4, 2024
1 parent accd220 commit 030431f
Showing 1 changed file with 61 additions and 35 deletions.
96 changes: 61 additions & 35 deletions greedy_algorithms/gale_shapley.cpp
View file
Original file line number Diff line number Diff line change
@@ -1,24 +1,26 @@
/**
* @file
* @brief [Gale Shapley Algorithm](https://en.wikipedia.org/wiki/Gale%E2%80%93Shapley_algorithm)
* @brief [Gale Shapley
* Algorithm](https://en.wikipedia.org/wiki/Gale%E2%80%93Shapley_algorithm)
* @details
* This implementation utilizes the Gale-Shapley algorithm to find stable matches.
* This implementation utilizes the Gale-Shapley algorithm to find stable
* matches.
*
* **Gale Shapley Algorithm** aims to find a stable matching between two equally sized
* sets of elements given an ordinal preference for each element. The algorithm was
* introduced by David Gale and Lloyd Shapley in 1962.
*
* Reference:
* **Gale Shapley Algorithm** aims to find a stable matching between two equally
* sized sets of elements given an ordinal preference for each element. The
* algorithm was introduced by David Gale and Lloyd Shapley in 1962.
*
* Reference:
* [Wikipedia](https://en.wikipedia.org/wiki/Gale%E2%80%93Shapley_algorithm)
* [Wikipedia](https://en.wikipedia.org/wiki/Stable_matching_problem)
*
* @author [B Karthik](https://github.com/BKarthik7)
*/

#include <iostream> /// for std::u32int_t
#include <vector> /// for std::vector
#include <algorithm> /// for std::find
#include <cassert> /// for assert
#include <cstdint> /// for std::uint32_t
#include <vector> /// for std::vector

/**
* @namespace
Expand All @@ -31,19 +33,25 @@ namespace greedy_algorithms {
*/
namespace stable_matching {
/**
* @brief The main function that finds the stable matching between two sets of elements
* using the Gale-Shapley Algorithm.
* @note This doesn't work on negative preferences. the preferences should be continuous integers starting from
* 0 to number of preferences - 1.
* @param primary_preferences the preferences of the primary set should be a 2D vector
* @param secondary_preferences the preferences of the secondary set should be a 2D vector
* @brief The main function that finds the stable matching between two sets of
* elements using the Gale-Shapley Algorithm.
* @note This doesn't work on negative preferences. the preferences should be
* continuous integers starting from 0 to number of preferences - 1.
* @param primary_preferences the preferences of the primary set should be a 2D
* vector
* @param secondary_preferences the preferences of the secondary set should be a
* 2D vector
* @returns matches the stable matching between the two sets
*/
std::vector<std::uint32_t> gale_shapley(const std::vector<std::vector<std::uint32_t>>& secondary_preferences, const std::vector<std::vector<std::uint32_t>>& primary_preferences) {
std::vector<std::uint32_t> gale_shapley(
const std::vector<std::vector<std::uint32_t>>& secondary_preferences,
const std::vector<std::vector<std::uint32_t>>& primary_preferences) {
std::uint32_t num_elements = secondary_preferences.size();
std::vector<std::uint32_t> matches(num_elements, -1);
std::vector<bool> is_free_primary(num_elements, true);
std::vector<std::uint32_t> proposal_index(num_elements, 0); // Tracks the next secondary to propose for each primary
std::vector<std::uint32_t> proposal_index(
num_elements,
0); // Tracks the next secondary to propose for each primary

while (true) {
int free_primary_index = -1;
Expand All @@ -57,10 +65,13 @@ std::vector<std::uint32_t> gale_shapley(const std::vector<std::vector<std::uint3
}

// If no free primary is found, break the loop
if (free_primary_index == -1) break;
if (free_primary_index == -1)
break;

// Get the next secondary to propose
std::uint32_t secondary_to_propose = primary_preferences[free_primary_index][proposal_index[free_primary_index]];
std::uint32_t secondary_to_propose =
primary_preferences[free_primary_index]
[proposal_index[free_primary_index]];
proposal_index[free_primary_index]++;

// Get the current match of the secondary
Expand All @@ -72,18 +83,21 @@ std::vector<std::uint32_t> gale_shapley(const std::vector<std::vector<std::uint3
is_free_primary[free_primary_index] = false;
} else {
// Determine if the current match should be replaced
auto new_proposer_rank = std::find(secondary_preferences[secondary_to_propose].begin(),
secondary_preferences[secondary_to_propose].end(),
free_primary_index);
auto current_match_rank = std::find(secondary_preferences[secondary_to_propose].begin(),
secondary_preferences[secondary_to_propose].end(),
current_match);
auto new_proposer_rank =
std::find(secondary_preferences[secondary_to_propose].begin(),
secondary_preferences[secondary_to_propose].end(),
free_primary_index);
auto current_match_rank =
std::find(secondary_preferences[secondary_to_propose].begin(),
secondary_preferences[secondary_to_propose].end(),
current_match);

// If the new proposer is preferred over the current match
if (new_proposer_rank < current_match_rank) {
matches[secondary_to_propose] = free_primary_index;
is_free_primary[free_primary_index] = false;
is_free_primary[current_match] = true; // Current match is now free
is_free_primary[current_match] =
true; // Current match is now free
}
}
}
Expand All @@ -99,31 +113,43 @@ std::vector<std::uint32_t> gale_shapley(const std::vector<std::vector<std::uint3
*/
static void tests() {
// Test Case 1
std::vector<std::vector<std::uint32_t>> primary_preferences = {{0, 1, 2, 3}, {2, 1, 3, 0}, {1, 2, 0, 3}, {3, 0, 1, 2}};
std::vector<std::vector<std::uint32_t>> secondary_preferences = {{1, 0, 2, 3}, {3, 0, 1, 2}, {0, 2, 1, 3}, {1, 2, 0, 3}};
assert(greedy_algorithms::stable_matching::gale_shapley(secondary_preferences, primary_preferences) == std::vector<std::uint32_t>({0, 2, 1, 3}));
std::vector<std::vector<std::uint32_t>> primary_preferences = {
{0, 1, 2, 3}, {2, 1, 3, 0}, {1, 2, 0, 3}, {3, 0, 1, 2}};
std::vector<std::vector<std::uint32_t>> secondary_preferences = {
{1, 0, 2, 3}, {3, 0, 1, 2}, {0, 2, 1, 3}, {1, 2, 0, 3}};
assert(greedy_algorithms::stable_matching::gale_shapley(
secondary_preferences, primary_preferences) ==
std::vector<std::uint32_t>({0, 2, 1, 3}));

// Test Case 2
primary_preferences = {{0, 2, 1, 3}, {2, 3, 0, 1}, {3, 1, 2, 0}, {2, 1, 0, 3}};
secondary_preferences = {{1, 0, 2, 3}, {3, 0, 1, 2}, {0, 2, 1, 3}, {1, 2, 0, 3}};
assert(greedy_algorithms::stable_matching::gale_shapley(secondary_preferences, primary_preferences) == std::vector<std::uint32_t>({0, 3, 1, 2}));
primary_preferences = {
{0, 2, 1, 3}, {2, 3, 0, 1}, {3, 1, 2, 0}, {2, 1, 0, 3}};
secondary_preferences = {
{1, 0, 2, 3}, {3, 0, 1, 2}, {0, 2, 1, 3}, {1, 2, 0, 3}};
assert(greedy_algorithms::stable_matching::gale_shapley(
secondary_preferences, primary_preferences) ==
std::vector<std::uint32_t>({0, 3, 1, 2}));

// Test Case 3
primary_preferences = {{0, 1, 2}, {2, 1, 0}, {1, 2, 0}};
secondary_preferences = {{1, 0, 2}, {2, 0, 1}, {0, 2, 1}};
assert(greedy_algorithms::stable_matching::gale_shapley(secondary_preferences, primary_preferences) == std::vector<std::uint32_t>({0, 2, 1}));
assert(greedy_algorithms::stable_matching::gale_shapley(
secondary_preferences, primary_preferences) ==
std::vector<std::uint32_t>({0, 2, 1}));

// Test Case 4
primary_preferences = {};
secondary_preferences = {};
assert(greedy_algorithms::stable_matching::gale_shapley(secondary_preferences, primary_preferences) == std::vector<std::uint32_t>({}));
assert(greedy_algorithms::stable_matching::gale_shapley(
secondary_preferences, primary_preferences) ==
std::vector<std::uint32_t>({}));
}

/**
* @brief Main function
* @returns 0 on exit
*/
int main() {
tests(); // Run self-test implementations
tests(); // Run self-test implementations
return 0;
}

0 comments on commit 030431f

Please sign in to comment.