2D Arrays

🔢 2D Array Algorithms

Part 1 of 7 — Row/Column Processing, Searching, and Modifying

Processing Individual Rows or Columns

Sum of a Specific Row

public int rowSum(int[][] matrix, int row) {
    int sum = 0;
    for (int c = 0; c < matrix[row].length; c++) {
        sum += matrix[row][c];
    }
    return sum;
}

Sum of a Specific Column

public int colSum(int[][] matrix, int col) {
    int sum = 0;
    for (int r = 0; r < matrix.length; r++) {
        sum += matrix[r][col];
    }
    return sum;
}

🔑 Row processing fixes the row index and loops over columns. Column processing fixes the column index and loops over rows.

Finding a Value in a 2D Array

public boolean contains(int[][] matrix, int target) {
    for (int r = 0; r < matrix.length; r++) {
        for (int c = 0; c < matrix[r].length; c++) {
            if (matrix[r][c] == target) {
                return true;
            }
        }
    }
    return false;
}

Concept Check 🎯

Modifying 2D Array Elements

Multiply All Elements by 2

for (int r = 0; r < matrix.length; r++) {
    for (int c = 0; c < matrix[r].length; c++) {
        matrix[r][c] *= 2;
    }
}

Replace Negatives with Zero

for (int r = 0; r < matrix.length; r++) {
    for (int c = 0; c < matrix[r].length; c++) {
        if (matrix[r][c] < 0) {
            matrix[r][c] = 0;
        }
    }
}

Diagonal Elements

// Main diagonal (row == col): top-left to bottom-right
// Only works for square matrices!
for (int i = 0; i < matrix.length; i++) {
    System.out.println(matrix[i][i]);
}

Edge Elements (Border)

// An element is on the edge if:
// r == 0 (first row), r == rows-1 (last row),
// c == 0 (first col), c == cols-1 (last col)
for (int r = 0; r < matrix.length; r++) {
    for (int c = 0; c < matrix[r].length; c++) {
        if (r == 0 || r == matrix.length - 1 ||
            c == 0 || c == matrix[r].length - 1) {
            // This element is on the border
        }
    }
}

Applied Recall ✍️

1. To process a single row, fix the _______ index and loop over columns.

2. Diagonal elements in a square matrix satisfy the condition row == _______.

3. An element is on the border of a 2D array if its row or column index equals 0 or the _______ valid index.

2D Array Algorithms 🔍

AP Exam Strategy: 2D Array Algorithms

• Row processing = fix row, vary column. Column processing = fix column, vary row
• Use matrix[r].length (not matrix[0].length) in the inner loop — handles jagged arrays
• Searching a 2D array is just nested linear search
• Know how to find: sum, average, max, min for the whole array, a specific row, or a specific column
• Diagonal, border, and neighbor-checking are common FRQ patterns
• When modifying elements, use standard for loops (not enhanced for)

AP-Style Application 🎯

💻 2D Array Algorithms

Part 2 of 7 — Key Processes

Understanding the processes related to 2D Array Algorithms helps explain how and why patterns develop. This part explores the mechanisms driving key phenomena.

Key Concepts

Concept Check 🎯

Key Processes — Deeper Dive

Process 1

The primary mechanism that drives patterns in 2D Array Algorithms. Understanding this concept is essential for mastering 2D Array Algorithms in AP Computer Science A.

Process 2

A secondary process that shapes outcomes in 2D Array Algorithms. This builds on the previous concept and connects to broader themes in the course.

Cause and effect

The relationship between actions and outcomes in 2D Array Algorithms. This is frequently tested on the AP exam and connects to multiple units in the curriculum.

Applied Recall (exact term answers) ✍️

1. What term refers to the primary mechanism that drives patterns in 2D Array Algorithms?

💻 2D Array Algorithms

Part 3 of 7 — Patterns & Examples

This part examines specific patterns and real-world examples related to 2D Array Algorithms. Case studies help illustrate abstract concepts.

Key Concepts

Concept Check 🎯

Patterns & Examples — Deeper Dive

Spatial pattern

The geographic distribution related to 2D Array Algorithms. Understanding this concept is essential for mastering 2D Array Algorithms in AP Computer Science A.

Case study

A specific real-world example that illustrates 2D Array Algorithms. This builds on the previous concept and connects to broader themes in the course.

Comparison

Analyzing similarities and differences across examples of 2D Array Algorithms. This is frequently tested on the AP exam and connects to multiple units in the curriculum.

Applied Recall (exact term answers) ✍️

1. What term refers to the geographic distribution related to 2D Array Algorithms?

💻 2D Array Algorithms

Part 4 of 7 — Connections & Interactions

2D Array Algorithms connects to other topics in AP Computer Science A. Understanding these connections reveals how different processes interact.

Key Concepts

Concept Check 🎯

Connections & Interactions — Deeper Dive

Interconnection

How 2D Array Algorithms links to other course topics. Understanding this concept is essential for mastering 2D Array Algorithms in AP Computer Science A.

Scale interaction

How 2D Array Algorithms operates differently at local, national, and global scales. This builds on the previous concept and connects to broader themes in the course.

Feedback loop

How outcomes of 2D Array Algorithms can reinforce or modify the original process. This is frequently tested on the AP exam and connects to multiple units in the curriculum.

Applied Recall (exact term answers) ✍️

1. What term refers to how 2D Array Algorithms links to other course topics?

💻 2D Array Algorithms

Part 5 of 7 — Change Over Time

2D Array Algorithms has evolved over time. Understanding historical and contemporary changes helps explain current patterns and predict future trends.

Key Concepts

Concept Check 🎯

Change Over Time — Deeper Dive

Continuity

Aspects of 2D Array Algorithms that have remained stable over time. Understanding this concept is essential for mastering 2D Array Algorithms in AP Computer Science A.

Change

How 2D Array Algorithms has transformed due to new forces and conditions. This builds on the previous concept and connects to broader themes in the course.

Trend

The direction of change in 2D Array Algorithms over time. This is frequently tested on the AP exam and connects to multiple units in the curriculum.

Applied Recall (exact term answers) ✍️

1. What term refers to aspects of 2D Array Algorithms that have remained stable over time?

💻 2D Array Algorithms

Part 6 of 7 — Problem-Solving Workshop

Apply 2D Array Algorithms concepts to data interpretation and analytical scenarios. Practice the types of questions seen on the AP exam.

Key Concepts

Concept Check 🎯

Problem-Solving Workshop — Deeper Dive

Data interpretation

Analyzing maps, graphs, and tables related to 2D Array Algorithms. Understanding this concept is essential for mastering 2D Array Algorithms in AP Computer Science A.

Argumentation

Making evidence-based claims about 2D Array Algorithms. This builds on the previous concept and connects to broader themes in the course.

Spatial reasoning

Using geographic thinking to analyze 2D Array Algorithms. This is frequently tested on the AP exam and connects to multiple units in the curriculum.

Applied Recall (exact term answers) ✍️

1. What term refers to analyzing maps, graphs, and tables related to 2D Array Algorithms?

💻 2D Array Algorithms

Part 7 of 7 — AP Review

Comprehensive review of 2D Array Algorithms for the AP exam. Focus on key concepts, common question types, and exam strategies.

Key Concepts

Concept Check 🎯

AP Review — Deeper Dive

Key vocabulary

Essential terms and definitions for 2D Array Algorithms. Understanding this concept is essential for mastering 2D Array Algorithms in AP Computer Science A.

Common question types

The most frequent ways 2D Array Algorithms is tested on the AP exam. This builds on the previous concept and connects to broader themes in the course.

Exam strategy

Approaches for answering 2D Array Algorithms questions effectively. This is frequently tested on the AP exam and connects to multiple units in the curriculum.

Applied Recall (exact term answers) ✍️

1. What term refers to essential terms and definitions for 2D Array Algorithms?

2. What concept describes the most frequent ways 2D Array Algorithms is tested on the AP exam?