CS 61A – Homework 1

1. Fill in the blanks in the following function definition for adding a to the absolute value of b, without calling abs.

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2. Write a function that takes three positive numbers and returns the sum of the squares of the two larger numbers. Use only a single expression for the body of the function:

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3. Let’s try to write a function that does the same thing as an if statement:

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This function actually doesn’t do the same thing as an if statement in all cases. To prove this fact, write functions c, t, and f such that one of these functions returns the number 1, but the other does not:

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4. Douglas Hofstadter’s Pulitzer-prize-winning book, Gödel, Escher, Bach, poses the following mathematical puzzle.

Pick a positive number n
If n is even, divide it by 2.
If n is odd, multiply it by 3 and add 1.
Continue this process until n is 1.
The number n will travel up and down but eventually end at 1 (at least for all numbers that have ever been tried — nobody has ever proved that the sequence will always terminate).

The sequence of values of n is often called a Hailstone sequence, because hailstones also travel up and down in the atmosphere before falling to earth. Write a function that takes a single argument with formal parameter name n, prints out the hailstone sequence starting at n, and returns the number of steps in the sequence:

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CS 61A – Homework 1

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