Largest triple product.

Author: deepakhb2

Problems/largest_triple_products.rb

@@ -0,0 +1,100 @@
+=begin
+Signature
+int[] find_max_product(int[] arr)
+Input
+n is in the range [1, 100,000].
+Each value arr[i] is in the range [1, 1,000].
+Output
+Return a list of n integers output[0..(n-1)], as described above.
+Example 1
+n = 5
+arr = [1, 2, 3, 4, 5]
+output = [-1, -1, 6, 24, 60]
+The 3rd element of output is 3*2*1 = 6, the 4th is 4*3*2 = 24, and the 5th is 5*4*3 = 60.
+Example 2
+n = 5
+arr = [2, 1, 2, 1, 2]
+output = [-1, -1, 4, 4, 8]
+The 3rd element of output is 2*2*1 = 4, the 4th is 2*2*1 = 4, and the 5th is 2*2*2 = 8.
+=end
+
+
+class Heap
+  attr_accessor :values
+  def initialize
+    @values = []
+  end
+
+  def push(value)
+    @values.push(value)
+  end
+
+  def pop(values)
+    @values.pop
+  end
+
+  def size
+    @values.size
+  end
+
+  def sum
+    @values.inject(1){|s, i| s*i}
+  end
+
+  def bubble_up
+    i = @values.size-1
+    while(i >= 1)
+      p = (i-1)/2
+      if @values[p] > @values[i]
+        @values[p], @values[i] = @values[i], @values[p]
+      end
+      i = p
+    end
+  end
+  
+  def heapify(i)
+    min = i
+    l = (2*i)+1
+    r = (2*i)+2
+    
+    if(l < @values.size && @values[l] < @values[min]) 
+      min = l
+    end
+  
+    if(r < @values.size && @values[r] < @values[min]) 
+      min = r
+    end
+    
+    if(min != i)
+      @values[i], @values[min] = @values[min], @values[i]
+      self.heapify(min); 
+    end   
+  end
+  
+  def remove_min
+    @values[0] = @values[@values.size-1]
+    @values.pop
+    self.heapify(0)
+  end
+end
+
+def find_max_product(arr)
+  min_heap = Heap.new
+  output = []
+  arr.each do |v|
+    if(min_heap.size < 2)
+      min_heap.push(v)
+      min_heap.bubble_up
+      output.push(-1)
+    else
+      min_heap.push(v)
+      min_heap.bubble_up
+      min_heap.remove_min if min_heap.size > 3
+      output.push(min_heap.sum)
+    end
+  end
+  return output
+end  
+
+# Call find_max_product() with test cases here 
+p find_max_product([1,2,3,4,5])