12Array

☕ Java Lesson – Arrays & 2D Arrays

Is lesson me hum seekhenge:

Array kya hota hai
Array creation & input utility
Array operations:
- Delete element
- Max & Min
- Merge sorted arrays
- Number occurrences
- Palindrome check
- Reverse array
- Array searching
- Sorted check
- Sum & Average
2D Arrays:
- Input & output
- Diagonal sum
- Sum & Average
- Search in 2D array
- Multidimensional arrays

📌 Array Kya Hota Hai?

Array ek container hai jisme same type ke multiple elements store kiye ja sakte hain.

Fixed size hota hai
Index 0 se start hota hai
Array me data contiguous memory me store hota hai

1️⃣ Array Creation

// 1D Array
int[] numbers = new int[5]; // size 5
int[] arr = {1,2,3,4,5};

// 2D Array
int[][] matrix = new int[3][3];
int[][] mat = { {1,2,3}, {4,5,6}, {7,8,9} };

2️⃣ Array Input Utility

import java.util.Scanner;

public class ArrayInput {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = 5;
        int[] arr = new int[n];

        System.out.println("Enter " + n + " numbers:");
        for(int i=0;i<n;i++){
            arr[i] = sc.nextInt();
        }

        System.out.println("Array elements:");
        for(int num : arr){
            System.out.print(num + " ");
        }
    }

}

3️⃣ Delete from Array (Shift Elements)

public class DeleteArray {

    static int[] deleteElement(int[] arr, int index){
        int n = arr.length;
        for(int i=index; i<n-1; i++){
            arr[i] = arr[i+1];
        }
        int[] newArr = new int[n-1];
        for(int i=0;i<n-1;i++){
            newArr[i] = arr[i];
        }
        return newArr;
    }

    public static void main(String[] args) {
        int[] arr = {1,2,3,4,5};
        arr = deleteElement(arr, 2); // delete index 2
        for(int num : arr) System.out.print(num + " ");
    }

}

Output:

1 2 4 5

4️⃣ Max & Min Number in Array

public class MaxMin {

    public static void main(String[] args) {
        int[] arr = {5,3,9,1,7};
        int max = arr[0];
        int min = arr[0];

        for(int num : arr){
            if(num > max) max = num;
            if(num < min) min = num;
        }

        System.out.println("Max = " + max);
        System.out.println("Min = " + min);
    }

}

5️⃣ Merge Two Sorted Arrays

public class MergeSorted {

    public static void main(String[] args) {

        int[] arr1 = {1,3,5};
        int[] arr2 = {2,4,6};
        int n1 = arr1.length;
        int n2 = arr2.length;
        int[] merged = new int[n1+n2];

        int i=0,j=0,k=0;

        while(i<n1 && j<n2){
            if(arr1[i] < arr2[j]) merged[k++] = arr1[i++];
            else merged[k++] = arr2[j++];
        }

        while(i<n1) merged[k++] = arr1[i++];
        while(j<n2) merged[k++] = arr2[j++];

        for(int num : merged) System.out.print(num + " ");
    }

}

Output:

1 2 3 4 5 6

6️⃣ Number Occurrences

public class Occurrence {

    static int countOccurrences(int[] arr, int x){
        int count = 0;
        for(int num : arr){
            if(num == x) count++;
        }
        return count;
    }

    public static void main(String[] args) {
        int[] arr = {1,2,3,2,4,2};
        System.out.println(countOccurrences(arr, 2)); // 3
    }

}

7️⃣ Palindrome Check (1D Array)

public class ArrayPalindrome {

    static boolean isPalindrome(int[] arr){
        int n = arr.length;
        for(int i=0;i<n/2;i++){
            if(arr[i] != arr[n-i-1]) return false;
        }
        return true;
    }

    public static void main(String[] args) {
        int[] arr = {1,2,3,2,1};
        System.out.println(isPalindrome(arr)); // true
    }

}

8️⃣ Reverse Array

public class ReverseArray {

    static void reverse(int[] arr){
        int n = arr.length;
        for(int i=0;i<n/2;i++){
            int temp = arr[i];
            arr[i] = arr[n-i-1];
            arr[n-i-1] = temp;
        }
    }

    public static void main(String[] args) {
        int[] arr = {1,2,3,4,5};
        reverse(arr);
        for(int num : arr) System.out.print(num + " ");
    }

}

Output:

5 4 3 2 1

9️⃣ Search in Array

public class SearchArray {

    static int search(int[] arr, int x){
        for(int i=0;i<arr.length;i++){
            if(arr[i]==x) return i;
        }
        return -1;
    }

    public static void main(String[] args) {
        int[] arr = {1,2,3,4,5};
        System.out.println(search(arr, 3)); // 2 (index)
    }

}

🔟 Check Sorted Array

public class SortedCheck {

    static boolean isSorted(int[] arr){
        for(int i=0;i<arr.length-1;i++){
            if(arr[i] > arr[i+1]) return false;
        }
        return true;
    }

    public static void main(String[] args) {
        int[] arr = {1,2,3,4,5};
        System.out.println(isSorted(arr)); // true
    }

}

1️⃣1️⃣ Sum & Average (1D Array)

public class SumAverage {

    static int sum(int[] arr){
        int s = 0;
        for(int num : arr) s += num;
        return s;
    }

    static double average(int[] arr){
        return (double)sum(arr)/arr.length;
    }

    public static void main(String[] args) {
        int[] arr = {1,2,3,4,5};
        System.out.println("Sum = " + sum(arr));
        System.out.println("Average = " + average(arr));
    }

}

1️⃣2️⃣ 2D Arrays – Input & Output

import java.util.Scanner;

public class TwoDArrayInput {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[][] matrix = new int[2][3];

        System.out.println("Enter 6 numbers:");
        for(int i=0;i<2;i++){
            for(int j=0;j<3;j++){
                matrix[i][j] = sc.nextInt();
            }
        }

        System.out.println("2D Array:");
        for(int i=0;i<2;i++){
            for(int j=0;j<3;j++){
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }

}

1️⃣3️⃣ Diagonal Sum (Square 2D Array)

public class DiagonalSum {

    public static void main(String[] args) {
        int[][] mat = { {1,2,3}, {4,5,6}, {7,8,9} };
        int sum = 0;
        for(int i=0;i<3;i++){
            sum += mat[i][i]; // main diagonal
        }
        System.out.println("Diagonal Sum = " + sum);
    }

}

Output:

Diagonal Sum = 15

1️⃣4️⃣ Sum & Average 2D Array

public class SumAverage2D {

    public static void main(String[] args) {
        int[][] mat = { {1,2}, {3,4} };
        int sum = 0, count = 0;
        for(int i=0;i<2;i++){
            for(int j=0;j<2;j++){
                sum += mat[i][j];
                count++;
            }
        }
        System.out.println("Sum = " + sum);
        System.out.println("Average = " + (double)sum/count);
    }

}

1️⃣5️⃣ Search in 2D Array

public class Search2D {

    static boolean search(int[][] mat, int key){
        for(int i=0;i<mat.length;i++){
            for(int j=0;j<mat[0].length;j++){
                if(mat[i][j] == key) return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        int[][] mat = { {1,2,3}, {4,5,6} };
        System.out.println(search(mat, 5)); // true
    }

}

⚡ Important Points

Array ek homogeneous data structure hai
1D & 2D arrays index based access karte hain
Nested loops 2D array traversal ke liye important
Common operations:
- Sum, Average, Max, Min
- Reverse, Palindrome
- Search & Sorted check
- Merge, Occurrences

🎯 Interview Questions

1️⃣ Array kya hota hai?
2️⃣ 2D array me elements kaise access karte hain?
3️⃣ Array reverse aur palindrome kaise check karte hain?
4️⃣ Max & Min nikalne ka efficient method kya hai?
5️⃣ 2D array me diagonal sum kaise calculate karte hain?

🧾 Lesson Summary

Is lesson me humne seekha:

✔ 1D & 2D Arrays
✔ Array Input Utility
✔ Delete / Merge / Reverse / Palindrome / Occurrences
✔ Max & Min, Sum & Average
✔ Search & Sorted check
✔ Nested Loops for 2D Arrays
✔ Diagonal Sum, Sum & Average 2D array

Arrays Java ke fundamental data structure hai aur DSA ke liye basic concept hain.

🚀 Next Lesson

Next lesson me hum seekhenge:

Strings in Java
String methods
String manipulation
String challenges

Name		Name	Last commit message	Last commit date
parent directory ..
challanges		challanges
array.java		array.java
arraySearching.java		arraySearching.java
multidimensionalArray.java		multidimensionalArray.java
readme.md		readme.md

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

readme.md

☕ Java Lesson – Arrays & 2D Arrays

📌 Array Kya Hota Hai?

1️⃣ Array Creation

2️⃣ Array Input Utility

3️⃣ Delete from Array (Shift Elements)

4️⃣ Max & Min Number in Array

5️⃣ Merge Two Sorted Arrays

6️⃣ Number Occurrences

7️⃣ Palindrome Check (1D Array)

8️⃣ Reverse Array

9️⃣ Search in Array

🔟 Check Sorted Array

1️⃣1️⃣ Sum & Average (1D Array)

1️⃣2️⃣ 2D Arrays – Input & Output

1️⃣3️⃣ Diagonal Sum (Square 2D Array)

1️⃣4️⃣ Sum & Average 2D Array

1️⃣5️⃣ Search in 2D Array

⚡ Important Points

🎯 Interview Questions

🧾 Lesson Summary

🚀 Next Lesson

FilesExpand file tree

12Array

Directory actions

More options

Directory actions

More options

Latest commit

History

12Array

Folders and files

parent directory

readme.md

☕ Java Lesson – Arrays & 2D Arrays

📌 Array Kya Hota Hai?

1️⃣ Array Creation

2️⃣ Array Input Utility

3️⃣ Delete from Array (Shift Elements)

4️⃣ Max & Min Number in Array

5️⃣ Merge Two Sorted Arrays

6️⃣ Number Occurrences

7️⃣ Palindrome Check (1D Array)

8️⃣ Reverse Array

9️⃣ Search in Array

🔟 Check Sorted Array

1️⃣1️⃣ Sum & Average (1D Array)

1️⃣2️⃣ 2D Arrays – Input & Output

1️⃣3️⃣ Diagonal Sum (Square 2D Array)

1️⃣4️⃣ Sum & Average 2D Array

1️⃣5️⃣ Search in 2D Array

⚡ Important Points

🎯 Interview Questions

🧾 Lesson Summary

🚀 Next Lesson