Arrays – FRQ Practice (AP Computer Science A)

Arrays are one of the most important and frequently tested topics on the AP Computer Science A (AP CSA) exam.
They appear in both MCQs and FRQs and form the foundation for looping, indexing, searching, and algorithmic logic.

This page contains exam-style FRQs focused only on Arrays, written to match AP CSA difficulty and format.

Why Practice Arrays FRQs?

Arrays help build strong understanding of:

• Looping and iteration
• Index-based access
• Searching and counting
• Conditional logic
• Algorithmic thinking
• Common patterns like max/min, streaks, cumulative sum

Strong array logic leads to better performance on many FRQs.

How to Use This Page

• Try solving the question before checking the answer
• Compare your code with the model solution
• Read the “Common Mistakes” section for each problem
• Redo the problem to improve technique

FRQ 1 — Count Values Above a Threshold (Easy)

Problem:
Write a method countAbove(int[] arr, int limit) that returns how many elements in arr are strictly greater than limit.

Example:
arr = [30, 35, 28, 40], limit = 30 → output = 2

Approach

• Loop through all elements
• Use a counter
• Compare each value with the limit

Java Solution

public int countAbove(int[] arr, int limit) {
    int count = 0;
    for (int v : arr) {
        if (v > limit) {
            count++;
        }
    }
    return count;
}

Common Mistakes

• Using >= instead of >
• Forgetting that empty arrays return 0 automatically

FRQ 2 — First Index of Even Number (Easy)

Problem

Write firstEven(int[] nums) that returns the index of the first even number.
If none exist, return -1.

Example:
[3, 5, 8, 9] → returns 2

Approach

• Loop from start
• Check if each element is even
• Return index immediately

Java Solution

public int firstEven(int[] nums) {
    for (int i = 0; i < nums.length; i++) {
        if (nums[i] % 2 == 0) {
            return i;
        }
    }
    return -1;
}

Common Mistakes

• Returning the value instead of the index
• Using <= nums.length in the loop condition

FRQ 3 — Running Total Array (Medium)

Problem

Given an array, return a new array where each element is the sum of all previous elements including itself.

Example:
[2, 3, 5] → [2, 5, 10]

Approach

• Use a running sum variable
• Build a new array for output

Java Solution

public int[] runningTotal(int[] values) {
    int[] result = new int[values.length];
    int sum = 0;

    for (int i = 0; i < values.length; i++) {
        sum += values[i];
        result[i] = sum;
    }
    return result;
}

Common Mistakes

• Modifying the original array instead of returning a new one
• Forgetting that empty arrays return empty arrays

FRQ 4 — Replace Negatives With Zero (Medium)

Problem

Write fixNegatives(int[] arr) to replace every negative value with 0.
Modify the array directly (no return value needed).

Java Solution

public void fixNegatives(int[] arr) {
    for (int i = 0; i < arr.length; i++) {
        if (arr[i] < 0) {
            arr[i] = 0;
        }
    }
}

Common Mistakes

• Trying to remove negative elements (arrays can’t shrink)
• Using enhanced for-loop and trying to change values (it won’t modify arr)

FRQ 5 — Longest Increasing Streak (Hard)

Problem

Return the length of the longest strictly increasing streak in an array.

Example:
[3, 4, 5, 2, 3, 4, 6] → 4 (streak is 2, 3, 4, 6)

Approach

• Handle edge case of empty array
• Use two counters: current and longest
• Compare current element with previous one

Java Solution

public int longestIncreasingStreak(int[] arr) {
    if (arr.length == 0) return 0;

    int longest = 1;
    int current = 1;

    for (int i = 1; i < arr.length; i++) {
        if (arr[i] > arr[i - 1]) {
            current++;
        } else {
            longest = Math.max(longest, current);
            current = 1;
        }
    }
    return Math.max(longest, current);
}

Common Mistakes

• Resetting to 0 instead of 1
• Not returning 1 for single-element arrays

Next FRQ Topics

• ArrayList FRQ Practice
• Strings FRQ Practice
• Classes & Objects FRQ Practice
• 2D Arrays FRQ Practice
• Mixed Topic FRQs

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