count_bottom_leaves.rb

def count_bottom_leaves(binary_tree)
    return helper(binary_tree, get_depth_leaf(binary_tree)) 
end

def helper (binary_tree, bound_depth, depth=0)
    return 0 if(binary_tree == false)  
    
    left_node  = binary_tree[1]
    right_node = binary_tree[2]
    
    if(left_node == false && right_node == false)
        return bound_depth == depth + 1 ? 1 : 0
    else
        left_cbl  = helper(left_node, bound_depth, depth + 1)
        right_cbl = helper(right_node, bound_depth, depth + 1)
        
        return left_cbl + right_cbl
    end

    return 0        
end

def get_depth_leaf(binary_tree, depth=0)
    return depth if(binary_tree == false) 
    
    left_node    = binary_tree[1]
    right_node   = binary_tree[2]    
    
    left_depth  = get_depth_leaf(left_node, depth + 1)
    right_depth = get_depth_leaf(right_node, depth + 1)
    
    return left_depth > right_depth ? left_depth : right_depth    
end

puts count_bottom_leaves([2, [5, false, [7, false, false]], [9, false, false]]) # => 1
puts count_bottom_leaves([2, [5, false, [7, false, false]], [9, false, [11, false, false]]]) # => 2
puts count_bottom_leaves([2, [5, [6, false, false], [7, false, false]], [9, false, [11, false, false]]]) # => 3
puts count_bottom_leaves([2, [5, [6, false, false], [7, false, false]], [9, [10, false, false], [11, false, false]]]) # => 4
puts count_bottom_leaves([2, [5, [6, false, false], [7, false, false]], [9, false, false]]) # => 2
puts count_bottom_leaves([2, [5, [6, false, [20, false, false]], [7, false, false]], [9, [10, false, false], [11, false, false]]]) # => 1