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AP CSA Unit 6 Practice: Standard Array Algorithms MCQs

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AP CSA Practice: Standard Array Algorithms

📚 Topic 6.4 ⏱️ 15 Min Practice ✅ Updated for 2027 Exam

The AP Computer Science A exam does not just test if you know Java syntax; it tests if you can recognize standard logical patterns. Topic 6.4: Standard Algorithms covers the fundamental operations every programmer must memorize.

In this interactive practice set, you will trace code to identify what these common algorithms do. Being able to quickly spot a “find maximum” or “shift right” algorithm will save you massive amounts of time on the multiple-choice section.

Key Concepts to Remember Before You Start:

  • Min/Max Traps: When finding a minimum or maximum, always initialize your tracking variable to the first element of the array (e.g., int min = arr[0]), never to 0.
  • The Integer Division Trap: When calculating an average, remember that dividing an int sum by an int length results in truncation. You must cast one to a double.
  • Swapping Elements: Reversing an array requires a temporary variable (temp) to hold data so it isn’t overwritten.
  • Index Bounds: When comparing adjacent elements (like arr[i] and arr[i+1]), your loop must stop at length - 1 to prevent an ArrayIndexOutOfBoundsException.

Test your algorithm tracing skills with the 10 practice questions below!

Topic 6.4 Practice

Question 1 of 10 | Score: 0
1. Consider the following method designed to find the minimum value in an array:
public int findMin(int[] arr) {
    int min = 0;
    for (int i = 0; i < arr.length; i++) {
        if (arr[i] < min) {
            min = arr[i];
        }
    }
    return min;
}
Under which condition will this method FAIL to return the correct minimum value?
Correct Answer: C This is a classic AP trap! If min is initialized to 0, and the array only contains positive numbers (e.g., {5, 10, 15}), the condition arr[i] < min will never be true. The method will incorrectly return 0. The correct initialization should always be int min = arr[0];.
2. Consider the following code segment:
int[] arr = {2, 5, 8, 3};
double avg = 0.0;
int sum = 0;
for (int num : arr) {
    sum += num;
}
avg = sum / arr.length;
System.out.println(avg);
What is printed as a result of executing the code segment?
Correct Answer: A The sum is 18, and the length is 4. Because sum is an int and arr.length is an int, Java performs integer division: 18 / 4 truncates to 4. That integer 4 is then cast to the double 4.0 to be stored in avg. To fix this, you must cast one side to a double before dividing: (double) sum / arr.length.
3. Consider the following array reversal algorithm:
int[] nums = {1, 2, 3, 4, 5};
for (int i = 0; i < nums.length / 2; i++) {
    int temp = nums[i];
    nums[i] = nums[nums.length - 1 - i];
    nums[nums.length - 1 - i] = temp;
}
What are the contents of the array after this code executes?
Correct Answer: B This is the standard, perfectly executed array reversal algorithm. It loops exactly halfway through the array (nums.length / 2). During each iteration, it swaps the element at index i with its mirror counterpart at the end of the array using a temp variable.
4. What happens if the loop condition in the previous array reversal algorithm is changed from i < nums.length / 2 to i < nums.length?
Correct Answer: A If you loop through the entire array while swapping, you will reverse the array in the first half of the loop, and then accidentally reverse it back to its original order during the second half of the loop!
5. Consider the following code segment:
int[] data = {10, 20, 30, 40};
for (int i = 0; i < data.length - 1; i++) {
    data[i] = data[i + 1];
}
What are the contents of the array after this code executes?
Correct Answer: B This algorithm shifts elements to the left. data[0] becomes 20, data[1] becomes 30, and data[2] becomes 40. The loop stops at index 2 (because i < 3). The last element at index 3 is never overwritten, so it remains 40. This leaves a duplicate at the end.
6. Consider the following code segment designed to check if ALL elements in a boolean array are true:
boolean allTrue = true;
for (boolean b : flags) {
    if (!b) {
        allTrue = false;
    }
}
Which of the following describes the behavior of this algorithm?
Correct Answer: C This is a flawless "flag" algorithm. It assumes all elements are true initially. As it traverses the array, if it encounters even a single false element (!b), it flips the flag to false. Since it never flips back to true, it correctly identifies if ALL elements are true.
7. Consider the following method:
public boolean containsPair(int[] arr) {
    for (int i = 0; i < arr.length; i++) {
        if (arr[i] == arr[i + 1]) {
            return true;
        }
    }
    return false;
}
What is the problem with this method?
Correct Answer: A When you compare an element to the one next to it using arr[i + 1], your loop must stop one element early! The loop condition should be i < arr.length - 1. Because this loop goes all the way to the last index, checking arr[i + 1] on the last iteration will access memory out of bounds.
8. Consider the following algorithm intended to shift all elements one position to the right:
int[] arr = {1, 2, 3, 4};
for (int i = 0; i < arr.length - 1; i++) {
    arr[i + 1] = arr[i];
}
What are the contents of the array after execution?
Correct Answer: C This is a notoriously broken shift algorithm! In the first iteration, arr[1] becomes 1. The array is now {1, 1, 3, 4}. In the second iteration, arr[2] is overwritten by arr[1] (which is now 1!). This cascade effect overwrites every remaining element with the first element. To shift right, you must loop backwards!
9. Which code segment correctly checks if a string array words contains the target word "Java"?
Correct Answer: B When searching an array of Objects (like Strings), you must use `.equals()`, not `==` (which makes A wrong). Option C calls `.equals` on the array itself, not the element. Option D is a common trap: the `else return false;` will cause the method to quit and return false immediately if the very first element isn't a match.
10. Consider the following code snippet that counts elements:
int[] vals = {5, 10, 15, 20};
int count = 0;
for (int i = 0; i < vals.length; i++) {
    if (vals[i] > 10) {
        count++;
    }
}
System.out.println(count);
Which of the following enhanced for-loops produces the exact same output?
Correct Answer: B Option B is the correct translation. The loop variable v holds the actual value of the element, so you just compare v > 10. Option A attempts to use the value as an index (`vals[v]`), which will cause an OutOfBounds error.

Unit 6.4 Practice Complete!

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H2: The Integer Division Trap in Averages

If you missed Question 2, you fell for one of the most common mistakes in AP Computer Science A. When computing an average, you are usually adding up int values into an int sum, and then dividing by the length of the array (which is also an int).

In Java, an int divided by an int always throws away the decimal. By the time you assign the result to a double variable, the precision is already gone. Always remember to cast one of the numbers before dividing: double average = (double) sum / arr.length;.

Ready for the Ultimate Challenge?

You have learned how to create arrays, traverse them, and manipulate their data using standard algorithms. Now it is time to put everything together in a testing environment.

Take the final step in your Unit 6 review by moving on to our Unit 6 Mock Exam, featuring 15 exam-level questions mixing all of the concepts covered in this module.