HashTables.py changed

Author: armanjscript

DataStructures/Section7/HashTables.py

@@ -1,4 +1,4 @@
-#preventing collisions in hash ord by multiplying the ordinal numbers
+#minimizing collisions in hash ord by multiplying the ordinal numbers, but it has some collisions
 
 def myhash(item):
     mult=1
@@ -7,4 +7,75 @@ def myhash(item):
     for ch in item:
         hv += mult*ord(ch)
         mult+=1
-    return hv 
+    return hv 
+
+for item in ('hello world', 'world hello', 'gello xorld'):
+    print(f'hash function of {item}: {myhash(item)}')
+
+print("========================\n")
+
+#open addressing for eliminating collisions
+#linear probing, quadratic probing and double hashing
+
+class HashItem:
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+
+class HashTable:
+    def __init__(self):
+        self.size = 256
+        self.slots = [None for i in range(self.size)]
+        self.count = 0
+        self.MAXLOADFACTOR = 0.65 #maximum percentage of used slots for increasing the size of slots
+    
+    #just for internal use
+    def _hash(self, key):
+        hv = 0
+        mult = 1
+        for ch in key:
+            hv += mult * ord(ch)
+            mult += 1
+        return hv % self.size
+    
+    def put(self, key, value):
+        item = HashItem(key, value)
+        h = self._hash(key)
+        while self.slots[h] != None:
+            if self.slots[h].key == key:
+                break
+            h = (h + 1) % self.size
+        
+        if self.slots[h] == None:
+            self.count += 1
+            self.slots[h] = item
+            self.check_growth()
+    
+    def check_growth(self):
+        loadfactor = self.count / self.size
+        if loadfactor > self.MAXLOADFACTOR:
+            print("Load factor before growing the hash table", self.count / self.size )
+            self.growth()
+            print("Load factor after growing the hash table", self.count / self.size )
+    
+    def growth(self):
+        new_hash_table = HashTable()
+        new_hash_table.size = 2 * self.size
+        new_hash_table.slots = [None for i in range(new_hash_table.size)]
+
+        for i in range(self.size):
+            if self.slots[i] != None:
+                new_hash_table.put(self.slots[i].key, self.slots[i].value)
+        
+        self.size = new_hash_table.size
+        self.slots = new_hash_table.slots
+    
+ht = HashTable() 
+ht.put("good", "eggs") 
+ht.put("better", "ham") 
+ht.put("best", "spam") 
+ht.put("ad", "do not") 
+ht.put("ga", "collide")
+ht.put("awd", "do not") 
+ht.put("add", "do not") 
+ht.check_growth()