CodeU Session 1 Problems

Collatz.java

public class Collatz {
    //Consider a sequence of positive integers starting with x.If x is
    // even,the next integer in the sequence is x/2.If x is odd, the
    // next integer in the sequence is 3 * x + 1. The sequence stops when it
    // reaches1.
    //
    // For example, if x is 7, the sequence is
    //
    // 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1
    //
    // Fill in the function loopCount so that it returns the length of
    // the sequence starting from x.
    static int loopCount(int x) {
        //STUDENTS: FILL IN CODE HERE!
        return 0;
    }

    // Using loopCount, fill in the function maxLoop so that it returns
    // the maximum sequence length for any sequence that starts with a
    // number greater than or equal to x and less than y.
    static int maxLoop(int x, int y) {
        //STUDENTS: FILL IN CODE HERE!
        return 0;
    }

    public static void main(String[] args) {
        System.out.println(maxLoop(1, 100000));
    }
}

Filter.java

public class Filter {
    // Write a function named "evens" that takes as input an array of
    // ints and returns a different array of ints containing
    // only the even elements of the input.
    public static int[] evens(int[] input) {
        // Here are some reminders:
        //
        // You can find input's length using input.length.
        // You can find the remainder of a division using %. For instance,
        // 11 % 3 ⇒ 2
        // 25 % 4 ⇒ 1
        //
        // You can declare a new array of integers with the syntax:
        // int[]var_name = new int[n];
        //
        // For example:
        // int[] clown = new int[10]; //creates an array named clown of 10 integers(clown[0] through clown[9])
        //
        //STUDENTS,WRITE CODE HERE.

    }

    public static void main(String[] args) { //
        // Expected output:
        // test1 results:
        // 8
        // 6
        // 0
        // test2 results:
        // 2
        // 18
        // 28
        // 18
        // 28
        // 90
        // //STUDENTS, ADD ADDITIONAL TEST CASES BELOW
        int[] test1 = {8, 6, 7, 5, 3, 0, 9};
        int[] ans = evens(test1);
        System.out.println("test1results:");
        for (int i = 0; i < ans.length; ++i) {
            System.out.println(ans[i]);
        }
        int[] test2 = {2, 7, 18, 28, 18, 28, 45, 90, 45};
        ans = evens(test2);
        System.out.println("test2results:");
        for (int i = 0; i < ans.length; ++i) {
            System.out.println(ans[i]);
        }
    }
}

Zip.java

public class Zip {

    //Fill in the method "join". It returns a boolean array. The ith
    //value is that array(i.e.,array[i]) should be true if the ith
    //value in the first argument to join is divisible by the ith value
    //in the second argument to join. The returned boolean array should
    //be exactly as long as the shorter of the two arguments.
    //
    //Reminders:
    //
    // 1.An integer p is said to be "divisible by" an integer q when there
    // is some integer k such that q * k = p. This is the same as saying
    // "the remainder of p when divided by q is 0".
    // The remainder operator in Java is written with a percent sign:
    // "a%b" is the remainder of a when divided by b.
    //
    //2.The length of an array bar is stored in bar.length.
    //
    //3.New arrays are declared with the syntax:
    // float[]foo = new float[8];
    //

    static boolean[] join(int[] y, int[] z) {
        //STUDENTS: WRITE YOUR CODE HERE!
    }

    public static void main(String[] args) {

        //
        //Expected output:
        // false
        // false
        // false
        // false
        // true
        // false
        // true
        //

        //STUDENTS, ADD ADDITIONAL TEST CASES BELOW

        int euler[] = {2, 7, 18, 28, 18, 28, 45, 90, 45};

        int jenny[] = {8, 6, 7, 5, 3, 0, 9};

        boolean divisibles[] = join(euler, jenny);

        for(int i = 0; i < divisibles.length; ++i) {

            System.out.println(divisibles[i]);

        }

    }
}