Add py min pq

Author: awpala

python/data_structures/p165_min_pq.py

@@ -0,0 +1,39 @@
+'''
+    CLRS Exercise 6.5-3, p. 165
+'''
+
+from .p156_min_heap import MinHeap
+import math
+
+class MinPQ(MinHeap):
+    def __init__(self, A, heap_size):
+        super().__init__(A, heap_size)
+    
+    def heap_minimum(self):
+        return self.A[0]
+    
+    def heap_extract_min(self):
+        if self.heap_size < 1:
+            raise Exception('heap underflow')
+        min = self.heap_minimum()
+        self.A[0] = self.A.pop()
+        self.heap_size -= 1
+        self.min_heapify(0)
+        return min
+    
+    def heap_decrease_key(self, i, key):
+        if key > self.A[i]:
+            raise Exception('new key is larger than current key')
+        self.A[i] = key
+        while i > 0 and self.A[self.parent(i)] > self.A[i]:
+            self.A[i], self.A[self.parent(i)] = self.A[self.parent(i)], self.A[i]
+            i = self.parent(i)
+    
+    def min_heap_insert(self, key):
+        self.heap_size += 1
+        self.A.append(math.inf)
+        self.heap_decrease_key(self.heap_size - 1, key)
+    
+    # N.B. cf. Exercise 6.5-8, p. 166
+    def heap_delete(self, i):
+        pass # TO-DO

python/main.py

@@ -137,15 +137,35 @@
 A = [16, 14, 10, 8, 7, 9, 3, 2, 4, 1] # cf. Figure 6.5, p. 164
 max_pq = MaxPQ(A, len(A))
 max_pq.build_max_heap()
-print('\nafter buildMaxHeap:', max_pq.A)
+print('\nafter build_max_heap:', max_pq.A)
 max_pq.heap_increase_key(8, 15)
-print('after heapIncreaseKey(4 -> 15):', max_pq.A)
+print('after heap_increase_key(4 -> 15):', max_pq.A)
 
 A = [15, 13, 9, 5, 12, 8, 7, 4, 0, 6, 2, 1] # cf. Exercise 6.5-2, p. 165
 max_pq = MaxPQ(A, len(A))
 max_pq.build_max_heap()
-print('\nafter buildMaxHeap:', max_pq.A)
+print('\nafter build_max_heap:', max_pq.A)
 max_pq.max_heap_insert(10)
-print('after maxHeapInsert(10):', max_pq.A)
+print('after max_heap_insert(10):', max_pq.A)
 
 # TO-DO: fix heap_delete
+
+# CLRS Section 6.5 Exercises - Min Priority Queue
+from data_structures.p165_min_pq import MinPQ
+A = []
+
+print('\nExercise 6.5-3 - Min Priority Queue')
+
+A = [16, 14, 10, 8, 7, 9, 3, 2, 4, 1] # cf. Figure 6.5, p. 164
+min_pq = MinPQ(A, len(A))
+min_pq.build_min_heap()
+print('\nafter build_min_heap:', min_pq.A)
+min_pq.heap_decrease_key(8, 15)
+print('after heap_decrease_key(4 -> 15):', min_pq.A)
+
+A = [15, 13, 9, 5, 12, 8, 7, 4, 0, 6, 2, 1] # cf. Exercise 6.5-2, p. 165
+min_pq = MinPQ(A, len(A))
+min_pq.build_min_heap()
+print('\nafter build_min_heap:', min_pq.A)
+min_pq.min_heap_insert(10)
+print('after min_heap_insert(10):', min_pq.A)