cleanup algs and hash tables

Algorithms/datastructs/hash_table.py

@@ -0,0 +1,66 @@
+import random
+
+class RandomizedSet:
+
+    def __init__(self):
+        self.hash_table = dict()
+        self.lst = []
+    def insert(self, val: int) -> bool:
+        if val not in self.hash_table:
+            self.hash_table[val] = len(self.lst)
+            self.lst.append(val)
+            return True
+        else:
+            return False
+    def remove(self, val: int) -> bool:
+        if val in self.hash_table:
+            idx = self.hash_table.pop(val)
+            # swap if index is not last
+            if idx != len(self.lst)-1:
+                last = self.lst[-1]
+                self.lst[-1] = self.lst[idx]
+                self.lst[idx] = last
+                self.hash_table[last] = idx
+            self.lst.pop()
+            return True
+        else:
+            return False
+    def getRandom(self) -> int:
+        if not self.lst:
+            raise IndexError("getRandom() called on empty set")
+        return self.lst[random.randint(0, len(self.lst) - 1)]
+
+class RandomizedCollection:
+
+    def __init__(self):
+        self.table = dict()
+        self.lst = []
+
+    def insert(self, val: int) -> bool:
+        self.lst.append(val)
+        if val not in self.table:
+            self.table[val] = {len(self.lst)-1}
+            return True
+        else:
+            self.table[val].add(len(self.lst)-1)
+            return False
+
+    def remove(self, val: int) -> bool:
+        if val in self.table:
+            idx = self.table[val].pop()
+            if idx != len(self.lst)-1:
+                # not last
+                last = self.lst[-1]
+                self.lst[-1] = self.lst[idx]
+                self.lst[idx] = last
+                self.table[last].remove(len(self.lst)-1)
+                self.table[last].add(idx)
+            self.lst.pop()
+            if not self.table[val]:
+                del self.table[val]
+            return True
+        else:
+            return False
+
+    def getRandom(self) -> int:
+        return self.lst[random.randint(0, len(self.lst)-1)]

tests/test_hash_table.py

@@ -0,0 +1,40 @@
+from Algorithms.datastructs.hash_table import RandomizedSet
+
+def test_randomized_set():
+    rs = RandomizedSet()
+
+    # Insert 0, should return True
+    assert rs.insert(0) == True
+    # Remove 0, should return True
+    assert rs.remove(0) == True
+    # Remove 0 again, should return False (already removed)
+    assert rs.remove(0) == False
+    # Insert 0 again, should return True
+    assert rs.insert(0) == True
+    # getRandom should return 0 (only element)
+    assert rs.getRandom() == 0
+    # Remove 0, should return True
+    assert rs.remove(0) == True
+    # Insert -1, should return True
+    assert rs.insert(-1) == True
+    # Remove 0 (not present), should return False
+    assert rs.remove(0) == False
+
+    # Multiple getRandom calls — since only -1 is present, it should always return -1
+    for _ in range(10):
+        val = rs.getRandom()
+        assert val == -1, f"Expected -1 but got {val}"
+
+    # Remove -1, should return True
+    assert rs.remove(-1) == True
+    # Now getRandom on empty set — handle gracefully by catching exception or custom behavior
+    try:
+        rs.getRandom()
+        print("getRandom on empty set did not raise error — consider adding handling for empty set.")
+    except IndexError:
+        print("getRandom on empty set raised IndexError as expected.")
+
+    print("All tests passed!")
+
+if __name__ == "__main__":
+    test_randomized_set()