Fall 21 [Bono]

CS 455 Midterm 1 Solution

Problem 1

Part A.

Part B.

[26, 32] [26, 32]

Problem 2

Part A constructor getLoc getDir

Part B Solution shown in bold

// Ant that can move around in a two-dimensional world.

public class Ant2D {

public static final int NORTH = 0;
public static final int EAST = 1;
public static final int SOUTH = 2;
public static final int WEST = 3;
public static final int NUM_DIRECTIONS = 4;

private Point currLoc;

private int currDirection;

// Create a ant at location startPos, facing EAST
public Ant2D(Point startPos) {

currLoc = new Point(startPos);

currDirection = EAST;

}

// Get ant’s current position
public Point getLoc() {

return currLoc;

}

// Get ant's current direction
// Returns one of NORTH, EAST, SOUTH, or WEST
public int getDir() {

return currDirection;

}

// Turn ant right by 90 degrees
public void turnRight() {

currDirection++;

if (currDirection == NUM_DIRECTIONS) {

currDirection = NORTH;

}

}

// Advance the ant forward by distance units in the direction
// he is facing
// PRE: distance >= 0 [ he can't go backwards ]
public void advance(int distance) {

if (currDirection == NORTH) {

currDir.translate(0, -distance);

} else if (currDirection == EAST) {

currDir.translate(distance, 0);

} else if (currDirection == SOUTH) {

currDir.translate(0, distance);

} else if (currDirection == WEST) {

currDir.translate(-distance, 0);

}

}

}

Problem 3 Several correct solutions (two given here)

mkdir 09-16

cp $ASNLIB/public/09-16/* 09-16

The following 1-line solution uses cp -r (recursive copy):

cp -r $ASNLIB/public/09-16 .

Problem 4

Part A.

bottom width scale

Part B.

bottom left scale

Part C.

applicationHeight label

Problem 5 Changes shown in bold
Part A

public class Square {

private int length;
private int area;

// create a square with given length for a side
public Square(int sideLength) {
length = sideLength;
area = sideLength*sideLength;

}

// get the area of the square
public int getArea() { return area; }

// double the length of each side
public void grow() {

length = 2 * length;

area = length * length;

}
}

Problem 5
Part B

public class Square {

private int length;

private int area;

// create a square with given length for a side
public Square(int sideLength) {

length = sideLength;

area = sideLength*sideLength;

}

// get the area of the square
public int getArea() {

return area;

return length * length;

}

// double the length of each side
public void grow() { length = 2 * length; }

}

Problem 6

Part A Several possible solutions. Two of them shown below.

// Solution 1: this solution iterates over result

public static double[] neighborAverage(int[] nums) {

assert nums.length > 0 && nums.length % 3 == 0; // optional

double[] result = new double[nums.length / 3];

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

result[i] = (nums[i*3] + nums[i*3+1] + nums[i*3 +2]) / 3.0;

}

return result;

}

// Solution 2: this solution iterates over nums
public static double[] neighborAverage2(int[] nums) {
 assert nums.length > 0 && nums.length % 3 == 0; // optional

 
 double[] result = new double[nums.length / 3];
 // (i < nums.length - 2) also works below
 for (int i = 0; i < nums.length; i+=3) {
  result[i/3] = (nums[i] + nums[i+1] + nums[i + 2]) / 3.0;
 } 
 return result;
}

Part B

assert nums.length > 0 && nums.length % 3 == 0;