🔄 Reverse an Array – Python Solution

Hi All,

Today I worked on a basic but important problem: Reversing an Array.

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📌 Problem Statement

Given an array, reverse its elements such that:

• First element becomes last
• Second element becomes second-last
• And so on

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🔍 Example

Example 1:

arr = [1, 4, 3, 2, 6, 5]

Output:

[5, 6, 2, 3, 4, 1]

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Example 2:

arr = [4, 5, 1, 2]

Output:

[2, 1, 5, 4]

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💡 Approach

🔹 Method 1: Using Two Pointers (Optimal)

• Use two pointers:
  • start → beginning of array
  • end → last index
• Swap elements until they meet

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💻 Python Code (Two Pointer Method)

def reverse_array(arr):
    start = 0
    end = len(arr) - 1

    while start < end:
        arr[start], arr[end] = arr[end], arr[start]
        start += 1
        end -= 1

    return arr

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🔍 Dry Run

For:

arr = [1, 4, 3, 2]

Steps:

• Swap 1 and 2 → [2, 4, 3, 1]
• Swap 4 and 3 → [2, 3, 4, 1]

Final Output:

[2, 3, 4, 1]

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🖥️ Sample Output

Input: [1, 4, 3, 2, 6, 5]
Output: [5, 6, 2, 3, 4, 1]

Input: [4, 5, 1, 2]
Output: [2, 1, 5, 4]

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🧠 Alternative Methods

🔹 Method 2: Using Slicing

def reverse_array(arr):
    return arr[::-1]

👉 Very simple but uses extra space

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🔹 Method 3: Using reverse()

arr.reverse()

👉 Modifies the original array

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⚡ Complexity Analysis

Method	Time	Space
Two Pointer	O(n)	O(1) ✅
Slicing	O(n)	O(n) ❌

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✅ Conclusion

This problem helped me understand:

• Two pointer technique
• In-place array manipulation
• Different ways to reverse data

🚀 This is a fundamental concept used in many problems!

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