diff --git a/lib/min_heap.rb b/lib/min_heap.rb index 6eaa630..e91a056 100644 --- a/lib/min_heap.rb +++ b/lib/min_heap.rb @@ -14,18 +14,23 @@ def initialize end # This method adds a HeapNode instance to the heap - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n(log(n))) where n is the number of nodes in the heap + # Space Complexity: O(1) def add(key, value = key) - raise NotImplementedError, "Method not implemented yet..." + heap_node = HeapNode.new(key, value) + @store << heap_node + heap_up(@store.length - 1) end # This method removes and returns an element from the heap # maintaining the heap structure - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(logn) where n is the number of elements in the heap + # Space Complexity: O(1) def remove() - raise NotImplementedError, "Method not implemented yet..." + swap(0, @store.length - 1) + removed = @store.pop + heap_down(0) + return removed.value end @@ -55,17 +60,41 @@ def empty? # This helper method takes an index and # moves it up the heap, if it is less than it's parent node. # It could be **very** helpful for the add method. - # Time complexity: ? - # Space complexity: ? + # Time complexity: O(logn) where n is the number of nodes in the tree + # Space complexity: O(1) def heap_up(index) + return if index == 0 + current_index = index + parent_index = (index - 1) / 2 + return if @store[current_index].key > @store[parent_index].key + + swap(current_index, parent_index) + heap_up(parent_index) end # This helper method takes an index and # moves it up the heap if it's smaller # than it's parent node. def heap_down(index) - raise NotImplementedError, "Method not implemented yet..." + current_index = index + left_child_index = index * 2 + 1 + right_child_index = index * 2 + 2 + + return unless @store[left_child_index] # we're at the bottom of the tree (could also use length) + + if @store[right_child_index] + if @store[left_child_index].key < @store[right_child_index].key + swap(current_index, left_child_index) + heap_down(left_child_index) + else + swap(current_index, right_child_index) + heap_down(right_child_index) + end + else + swap(current_index, left_child_index) + return + end end # If you want a swap method... you're welcome