Day 2 Java Arrays

✅ Day 2: Arrays – Traversals, Operations & Basic Problems

🎯 Goals of the Day

• Understand 1D array declaration and initialization in Java

• Learn array traversal techniques

• Solve beginner-level problems on arrays

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📘 1. Arrays in Java – The Basics

An array is a collection of elements of the same type stored in contiguous memory.

🔹 Declaration:

int[] arr = new int[5];           // creates an array of size 5
int[] nums = {1, 2, 3, 4, 5};     // directly initialized

🔹 Access:

System.out.println(arr[0]);       // prints the first element
arr[2] = 10;                      // sets the third element to 10

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🔁 2. Traversal of Arrays

🔹 Using For Loop:

for (int i = 0; i < arr.length; i++) {
    System.out.println(arr[i]);
}

🔹 Using Enhanced For Loop:

for (int num : arr) {
    System.out.println(num);
}

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✍️ 3. Input in Arrays

Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int[] arr = new int[n];

for (int i = 0; i < n; i++) {
    arr[i] = sc.nextInt();
}

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🔎 4. Basic Problems to Practice

🧠 Problem 1: Find the maximum element in an array

int max = arr[0];
for (int i = 1; i < arr.length; i++) {
    if (arr[i] > max) max = arr[i];
}
System.out.println("Max: " + max);

🧠 Problem 2: Reverse the array

int start = 0, end = arr.length - 1;
while (start < end) {
    int temp = arr[start];
    arr[start] = arr[end];
    arr[end] = temp;
    start++;
    end--;
}

🧠 Problem 3: Sum of all elements

int sum = 0;
for (int num : arr) {
    sum += num;
}
System.out.println("Sum = " + sum);

🧠 Problem 4: Check if array is sorted

boolean isSorted = true;
for (int i = 0; i < arr.length - 1; i++) {
    if (arr[i] > arr[i + 1]) {
        isSorted = false;
        break;
    }
}
System.out.println(isSorted ? "Sorted" : "Not Sorted");

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📚 5. Practice Questions for Today

Try solving these on any coding platform:

• Find the second largest element in an array

• Count frequency of an element in an array

• Left rotate an array by 1 position

• Move all 0s to the end of the array (maintaining order)

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🔥 Bonus Tip:

Create reusable methods in Java to solve problems:

public static int findMax(int[] arr) {
    int max = arr[0];
    for (int i = 1; i < arr.length; i++) {
        if (arr[i] > max) max = arr[i];
    }
    return max;
}