DoubleHashing.py finally approved

Author: armanjscript

DataStructures/Section7/DoubleHashing.py

@@ -0,0 +1,92 @@
+class HashItem:
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+
+class DoubleHashTable:
+    
+    def __init__(self):
+        self.size = 256
+        self.slots = [None for i in range(self.size)]
+        self.count = 0
+        self.MAXLOADFACTOR = 0.65
+        self.prime_num = 5
+    
+    #just for internal use (main hash function)
+    def _hash(self, key):
+        hv = 0
+        mult = 1
+        for ch in key:
+            hv += mult * ord(ch)
+            mult += 1
+        return hv % self.size
+    
+    #secondary hash function
+    def h2(self, key):
+        mult = 1
+        hv = 0
+        for ch in key:
+            hv += mult * ord(ch)
+            mult += 1
+        return hv
+    
+    def put(self, key, value):
+        item = HashItem(key, value)
+        h = self._hash(key)
+        j=1
+
+        while self.slots[h]!= None:
+            if self.slots[h].key == key:
+                break
+            h = (h + j * (self.prime_num - (self.h2(key) % self.prime_num))) % self.size
+            j = j+1
+        
+        if self.slots[h] == None:
+            self.count += 1
+        self.slots[h] = item
+        self.check_growth()
+
+    def get(self, key):
+        h = self._hash(key)
+        j = 1
+        while self.slots[h] != None:
+            if self.slots[h].key == key:
+                return self.slots[h].value
+            h = (h + j * (self.prime_num - (self.h2(key) % self.prime_num))) % self.size
+            j = j + 1
+        return None
+    
+    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 = DoubleHashTable() 
+ht.put("good", "eggs") 
+ht.put("better", "spam") 
+ht.put("best", "cool") 
+ht.put("ad", "donot") 
+ht.put("ga", "collide") 
+ht.put("awd", "hello") 
+ht.put("addition", "ok")
+
+for key in ("good", "better", "best", "worst", "ad", "ga"): 
+        v = ht.get(key) 
+        print(v) 
+print("The number of elements is: {}".format(ht.count))