Answers to common programming problems

gistfile1.txt

problem one
write three functions that compute the sum of the numbers in a given list
using a:

for loop
def sum(num1, num2, num3)
	numbers = [num1, num2, num3]
	total_sum = 0
	for num in numbers
		total_sum += num
	end 
	return total_sum
end 
print "\n"
print sum(1, 2, 3)
print "\n"

while-loop
def sum_with_while(num1, num2, num3)
	numbers = [num1, num2, num3]
	total_sum = 0 
	i = 0 
	while i < numbers.length do 
		total_sum += numbers[i]
		i += 1
		# print total_sum
	end 
	return total_sum
end 


recursion

def sum_recursion(num1, num2, num3)
	numbers = [num1, num2, num3]
	@total_sum = 0
	index = 0
	def add_numbers(numbers, index)
		if index >= numbers.length
			return @total_sum
		else
			@total_sum += numbers[index]
			index += 1
			add_numbers(numbers, index)
		end 
	end 
	add_numbers(numbers, index)
end 


PROBLEM 2 
Write a function that combines two lists by alternatingly taking elements
array_one = [1, 2, 3]
array_two = ['a', 'b', 'c']


def combine_arrays(array1, array2)
	array3 = []
	i = 0 
	while i < array1.length do 
		array3 << array1[i]
		array3 << array2[i]
		i += 1
	end 
	return array3
end 

print combine_arrays(array_one, array_two)

PROBLEM 3 

Write a function that computes the list of the first 100 Fibonacci numbers
(by definition, the first two numbers in the Fibonacci sequence are 0 and 1, 
each subsequent number is the sum of the previous two. 

def fibonacci_sequence
	fib_nums = [0, 1]
	until fib_nums.length == 100 do 
		last_num = fib_nums.length - 1
		second_last_num = fib_nums.length - 2
		new_num = fib_nums[last_num] + fib_nums[second_last_num]
		fib_nums << new_num
		
	end 	
	return fib_nums

end 
print fibonacci_sequence

PROBLEM 4 

Write a function that given a list of non-negative integers, arranges
them such that they form the largest possible number
Exampe: give [50, 2, 1, 9] the largest formed number is 95021

def generate_largest_number(array)
	permutations = array.permutation.to_a
	@largest_permutation
	i = 0 
	while i < permutations.length do 
		if i == 0 
			@largest_permutation = permutations[i].join
		else
			if permutations[i].join > @largest_permutation
				@largest_permutation = permutations[i].join
			end 
		end 
		i += 1
	end 
	return @largest_permutation		
end 
puts generate_largest_number([40, 9, 23, 21, 2])