Hackerrank Lambdas Solution

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Lambdas are anonymous functions. Lambdas in Ruby are objects of the class Proc.
They are useful in most of the situations where you would use a proc.

The simplest lambda takes no argument and returns nothing as shown below:

Example:

#Ruby version <= 1.8
    lambda { .... } 

    lambda do
        ....
    end

#Ruby version >= 1.9, "stabby lambda" syntax is added
    -> { .... }

    -> do
        ....
    end

Ruby version  can use both lambda and stabby lambda, ->.

Lambdas can be used as arguments to higher-order functions. They can also be used to construct the result of a higher-order function that needs to return a function.

Example:

_{(a). Lambda that takes no arguments.}

def area (l, b)
   -> { l * b } 
end

x = 10.0; y = 20.0

area_rectangle = area(x, y).call
area_triangle = 0.5 * area(x, y).()

puts area_rectangle     #200.0
puts area_triangle      #100.0

_{(b). Lambda that takes one or more arguments.}

area = ->(a, b) { a * b }

x = 10.0; y = 20.0

area_rectangle = area.(x, y)
area_triangle = 0.5 * area.call(x, y)

puts area_rectangle     #200.0
puts area_triangle      #100.0    

In the above example, we can see that lambdas can be called using both .call() and .().

Is there any difference between lambdas and procs?
Yes, there is difference between a proc and a lambda in Ruby.

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Task

You are given a partially complete code. Your task is to fill in the blanks (______).
There are  variables defined below:

• square is a lambda that squares an integer.
• plus_one is a lambda that increments an integer by .
• into_2 is a lambda that multiplies an integer by .
• adder is a lambda that takes two integers and adds them.
• values_only is a lambda that takes a hash and returns an array of hash values.

Solution in ruby

Approach 1.

# Write a lambda which takes an integer and square it
square      = -> (x) {x**2}

# Write a lambda which takes an integer and increment it by 1
plus_one    = -> (x) {x + 1}

# Write a lambda which takes an integer and multiply it by 2
into_2      = -> (x) {x * 2}

# Write a lambda which takes two integers and adds them
adder       = ->(x, y) {x + y}

# Write a lambda which takes a hash and returns an array of hash values
values_only = ->(hash) { hash.values}

input_number_1 = gets.to_i
input_number_2 = gets.to_i
input_hash = eval(gets)

a = square.(input_number_1); b = plus_one.(input_number_2);c = into_2.(input_number_1); 
d = adder.(input_number_1, input_number_2);e = values_only.(input_hash)

p a; p b; p c; p d; p e

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Approach 2.

# Write a lambda which takes an integer and square it
square      = -> (n) {n*n}

# Write a lambda which takes an integer and increment it by 1
plus_one    = -> (n) {n+=1}

# Write a lambda which takes an integer and multiply it by 2
into_2      = -> (n) { n*2 }

# Write a lambda which takes two integers and adds them
adder       = -> (x, y) { x + y }

# Write a lambda which takes a hash and returns an array of hash values
values_only = -> (hash) {hash.values}


input_number_1 = gets.to_i
input_number_2 = gets.to_i
input_hash = eval(gets)

a = square.(input_number_1); b = plus_one.(input_number_2);c = into_2.(input_number_1); 
d = adder.(input_number_1, input_number_2);e = values_only.(input_hash)

p a; p b; p c; p d; p e

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Approach 3.

# Write a lambda which takes an integer and square it
square      = ->(i) { i * i } 

# Write a lambda which takes an integer and increment it by 1
plus_one    = ->(i) { i + 1} 

# Write a lambda which takes an integer and multiply it by 2
into_2      = ->(i) { i * 2 }

# Write a lambda which takes two integers and adds them
adder       = ->(a, b) { a + b }

# Write a lambda which takes a hash and returns an array of hash values
values_only = ->(h) { h.values }


input_number_1 = gets.to_i
input_number_2 = gets.to_i
input_hash = eval(gets)

a = square.(input_number_1); b = plus_one.(input_number_2);c = into_2.(input_number_1); 
d = adder.(input_number_1, input_number_2);e = values_only.(input_hash)

p a; p b; p c; p d; p e

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