Reverse an Array In Place

📌 Definition:

📖 Detailed Explanation:

Swap elements from both ends toward the middle with two pointers — O(n) time, O(1) space. This is the array analog of string reversal and the building block for the rotate-by-k trick.

💻 Solutions:

• Java
• JavaScript
• Python

public static void reverse(int[] a) {
    int i = 0, j = a.length - 1;
    while (i < j) { int t = a[i]; a[i++] = a[j]; a[j--] = t; }
}

function reverse(a) {
  let i = 0, j = a.length - 1;
  while (i < j) { [a[i], a[j]] = [a[j], a[i]]; i++; j--; }
  return a;
}

def reverse(a):
    i, j = 0, len(a) - 1
    while i < j:
        a[i], a[j] = a[j], a[i]
        i += 1
        j -= 1
    return a

🔑 Key Points:

• Two pointers swapping toward the middle
• In place — O(1) extra space
• O(n) time
• Foundation for array rotation

🌍 Real-World Example: