Day 1 Basics of Java Arrays: Understand with Life Examples and Solve 15 LeetCode Challenges

“It’s not about the destination, it’s about the clarity you gain with every step.”
— The Peaceful Coder

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📅 Day 1 — Topic: Arrays

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🧠 Explanation

Imagine a row of empty tiffin boxes on your kitchen shelf.
Each box has a fixed position — Box 0, Box 1, Box 2...
You can fill them with anything: fruits, snacks, or even empty ones.
That, my friend, is an Array in programming.

Arrays are like those boxes — fixed-size containers storing similar items (numbers, strings, etc.), all lined up in order.

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🧪 Real-Life Example

Your shoe rack has 5 slots. You put 5 pairs of shoes in order.
Slot 0 → Sandals, Slot 1 → Sneakers...
You can directly go to Slot 3 and grab your formal shoes.

That's exactly how random access in arrays works:
You know the index, you get the value — instantly.

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🖼️ Image Reference

💻 Java Syntax (with comments)

// Declare an array of size 5
int[] shoes = new int[5];

// Assign values
shoes[0] = 1;  // sandals
shoes[1] = 2;  // sneakers

// Access value at index 1
System.out.println(shoes[1]);  // Output: 2

📋 Algorithm (How to Think About It)

• 🟡 Step 1: Declare an array of fixed size

• 🟢 Step 2: Use index (0-based) to insert values

• 🔵 Step 3: Access/update using the same index

• ⚪ Step 4: Loop through for any operation

🎯 Key Points to Remember

• Array size is fixed once declared.

• Indexing starts from 0.

• Can store only one data type.

• You get O(1) access time.

• Can't shrink/grow like magic — use ArrayList if needed.

📝 15 Beginner LeetCode Problems (Click to Practice)

Solution - Two Sum

class Solution {
    public int[] twoSum(int[] nums, int target) {
        for(int i=0;i<nums.length-1;i++)
        {
            for(int j=i+1;j<nums.length;j++)
            {
                if(nums[i]+nums[j]==target){
                     return new int[]{ i, j };
                }             
            }
        }
         return null;
    }   
}

Solution - Best Time to Buy and Sell Stock

class Solution {
    public int maxProfit(int[] prices) {
        int finalProfit=0;
        int minBuy=prices[0];
        for(int i=1;i<prices.length;i++){
            int profit=0;
            if(prices[i]-minBuy<0){
                minBuy=prices[i];
            }else{
                profit=prices[i]-minBuy;
                if(finalProfit<profit){
                    finalProfit=profit;
                }
            }
        }
        return finalProfit;
    }
}