Array Traversal: Looping Patterns and Techniques

1. The Hook (The "Byte-Sized" Intro)

In a Nutshell: Array traversal visits each element systematically.
Four patterns: for loop (index access), enhanced for (read-only), while loop, and reverse iteration.

When YouTube renders your subscription feed: for (Video v : subscriptions) display thumbnail. Every item, one by one!

2. Conceptual Clarity

💡 Traversal Patterns

graph LR Traversal["Traversal Types"] --> Forward["Forward<br/>0 → length-1"] Traversal --> Backward["Backward<br/>length-1 → 0"] Traversal --> ForEach["For-each<br/>Read-only"] Traversal --> While["While<br/>Conditional"]

3. Interactive & Applied Code

java

public class ArrayTraversal {
    public static void main(String[] args) {
        int[] nums = {10, 20, 30, 40, 50};
        
        // === FORWARD TRAVERSAL (for loop) ===
        System.out.println("Forward:");
        for (int i = 0; i < nums.length; i++) {
            System.out.println("Index " + i + ": " + nums[i]);
        }
        
        // === BACKWARD TRAVERSAL ===
        System.out.println("Backward:");
        for (int i = nums.length - 1; i >= 0; i--) {
            System.out.println("Index " + i + ": " + nums[i]);
        }
        
        // === ENHANCED FOR LOOP (read-only) ===
        System.out.println("For-each:");
        for (int num : nums) {
            System.out.println(num);
        }
        
        // === WHILE LOOP ===
        int i = 0;
        while (i < nums.length) {
            System.out.println(nums[i]);
            i++;
        }
        
        // === 2D ARRAY TRAVERSAL ===
        int[][] matrix = {{1, 2, 3}, {4, 5, 6}};
        
        // Row-by-row
        for (int row = 0; row < matrix.length; row++) {
            for (int col = 0; col < matrix[row].length; col++) {
                System.out.print(matrix[row][col] + " ");
            }
            System.out.println();
        }
        
        // Enhanced for (2D)
        for (int[] row : matrix) {
            for (int val : row) {
                System.out.print(val + " ");
            }
            System.out.println();
        }
        
        // === SKIP EVERY OTHER (Step 2) ===
        for (int j = 0; j < nums.length; j += 2) {
            System.out.println(nums[j]);  // 10, 30, 50
        }
        
        // === EARLY EXIT (break) ===
        for (int num : nums) {
            if (num == 30) break;  // Stop at 30
            System.out.println(num);
        }
        
        // === SKIP CERTAIN (continue) ===
        for (int num : nums) {
            if (num == 30) continue;  // Skip 30
            System.out.println(num);
        }
    }
}

⚠️ Common Mistakes

Mistake #1: Off-by-one in reverse

java

for (int i = arr.length; i >= 0; i--) // ❌ Starts out of bounds!
// Fix: i = arr.length - 1

Mistake #2: Modifying array in for-each

java

for (int num : nums) {
    num = num * 2;  // ❌ Modifies copy, not array!
}
// Use index-based for modification

4. The "Interview Corner"

🏆 Q1: "When to use for vs for-each?" Answer: for: need index or modification. for-each: read-only, cleaner.

🏆 Q2: "Traverse 2D array in spiral order?" Answer: Use four boundaries (top, bottom, left, right) and shrink after each pass. Common FAANG question!

🎓 Key Takeaways

✅ Forward: for (int i = 0; i < length; i++)
✅ Backward: for (int i = length-1; i >= 0; i--)
✅ For-each: read-only, cleaner syntax
✅ break/continue work in traversal
✅ 2D: nested loops for rows and columns

1. The Hook (The "Byte-Sized" Intro)

2. Conceptual Clarity

💡 Traversal Patterns

3. Interactive & Applied Code

⚠️ Common Mistakes

4. The "Interview Corner"

🎓 Key Takeaways

Topics Covered

Tags

Last Updated