Whiteboard Practice 1

Problems that focus on avoiding Ruby Magic and properly using Hashes and Arrays

For each of the following problems, you should write a single method to solve the problem. You will be working with arrays in each problem, but should use array indexing and loops to solve the problems. You should not utilize any Ruby Array methods, with the exception of <<, [], and .length.

e.g. NOT OK

• array.first ==> NOT OK
• array.insert(i, array2[loc]) ==> NOT OK
• array.pop ==> NOT OK
• array.uniq ==> NOT OK ;) See problem 3 and 4.

e.g. OK

• array[i] = array2[loc] ==> OK
• puts array[0] ==> OK
• array[-1] ==> OK

Problem #1

Write a method named print_array that accepts an array of integers as a parameter and that prints the contents of the array as a bracketed, comma-separated list.

For example, if a variable called list stores the following values: list = [3, 19, 27, 4, 98, 304, -9, 72]

Then the call of print(list) should produce the following output: [3, 19, 27, 4, 98, 304, -9, 72]

Your method should produce a single line of output (may wrap with long lists).

Problem #2

Write a method named stretch that accepts an array of integers as a parameter and returns a new array twice as large as the original, where every integer from the original array is replaced with a pair of integers, each half the original.

If a number in the original array is odd, then the first number in the new pair should be one higher than the second so that the sum equals the original number.

For example, if a variable named list refers to an array storing the values [18, 7, 4, 24, 11], the call of stretch(list) should return a new array containing [9, 9, 4, 3, 2, 2, 12, 12, 6, 5]. (The number 18 is stretched into the pair 9, 9, the number 7 is stretched into 4, 3, the number 4 is stretched into 2, 2, the number 24 is stretched into 12, 12 and the number 11 is stretched into 6, 5.)

Problem #3

Write a method named numUnique that accepts a sorted array of integers as a parameter and utilizes a hash to calculate and return the number of unique values in the array. The array is guaranteed to be in sorted order, which means that duplicates will be grouped together.

For example, if a variable called list stores the following values: list = [5, 7, 7, 7, 8, 22, 22, 23, 31, 35, 35, 40, 40, 40, 41] then the call of numUnique(list) should return 9 because this list has 9 unique values (5, 7, 8, 22, 23, 31, 35, 40 and 41).

It is possible that the list might not have any duplicates. For example if list instead stored this sequence of values: list = [1, 2, 11, 17, 19, 20, 23, 24, 25, 26, 31, 34, 37, 40, 41] Then a call on the method would return 15 because this list contains 15 different values.

If passed an empty list, your method should return 0.

Problem #4

Write a method named numUnique2 that functions the same as numUnique except that it does NOT use a hash to solve the problem. In this version, you should only iterate over the array, but use no auxiliary storage outside of fixnum variables, if needed.

Remember that you can assume that the values in the array appear in sorted (nondecreasing) order.