initial algorithm

Author: tomshalbar

greedy_methods/gale_shapley_stable_matching.py

@@ -0,0 +1,60 @@
+class GaleShapley:
+    """Implementation of the Gale-Shapley algorithem
+
+    takes it 2 preference list as a 2D array of ints. First one is the
+    proposing side.
+    """
+
+    def find_matches(
+        self,
+        proposers_preferences: dict[int, list[int]],
+        receivers_preferences: dict[int, list[int]],
+    ) -> dict[int, int]:
+        """
+        >>> gs = GaleShapley()
+        >>> gs.find_matches({1: [1, 2, 3], 2: [2, 1, 3], 3: [2, 3, 1]}, {1: [1, 2, 3], 2: [2, 1, 3], 3: [2, 3, 1]})
+        {1: 1, 2: 2, 3: 3}
+        >>> gs.find_matches({}, {})
+        {}
+        >>> gs.find_matches({1: [1,]}, {1: [1,]})
+        {1: 1}
+        """
+
+        matches = {key: -1 for key in proposers_preferences.keys()}
+
+        # [NOTE] I would've used sets, but want replicability for easy debugging.
+        free_proposers = list(proposers_preferences.keys())
+        tested_matches = {key: 0 for key in proposers_preferences.keys()}
+
+        while free_proposers:
+            proposer = free_proposers[0]
+
+            if tested_matches[proposer] == len(proposers_preferences[proposer]):
+                free_proposers.remove(proposer)
+                continue
+
+            receiver = proposers_preferences[proposer][tested_matches[proposer]]
+            tested_matches[proposer] += 1
+
+            if receiver not in matches.values():
+                matches[proposer] = receiver
+                free_proposers.remove(proposer)
+                continue
+            cur_proposer = next(
+                prop for prop, rec in matches.items() if rec == receiver
+            )
+            if receivers_preferences[receiver].index(proposer) < receivers_preferences[
+                receiver
+            ].index(cur_proposer):
+                matches[cur_proposer] = -1
+                matches[proposer] = receiver
+                free_proposers.remove(proposer)
+                free_proposers.append(cur_proposer)
+
+        return matches
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()