BL
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25. Reverse Array In-Place

Easy

Problem Description

Reverse an array of NN integers in-place using two pointers.

Input Format

  • •Line 1: An integer NN (1≤N≤1051 \le N \le 10^5).
  • •Line 2: NN space-separated integers A1,A2,…,ANA_1, A_2, \dots, A_N.

Output Format

Print the NN reversed integers separated by a single space.

Example 1:
Input:
5
1 2 3 4 5
Output:
5 4 3 2 1
Explanation: Reversing 1 2 3 4 5 yields 5 4 3 2 1.
Example 2:
Input:
1
99
Output:
99
Explanation: Single element remains unchanged.
Example 3:
Input:
4
10 20 30 40
Output:
40 30 20 10
Explanation: Even length array reversal.
Constraints:
  • Standard integer bounds: 32-bit signed integer or input range [1, 10^5].
  • Time complexity target: O(N) or O(N log N) where applicable.
  • Auxiliary space target: O(1) or minimal auxiliary memory.
Follow up:Can this algorithm be adapted to an online streaming setting where the entire input cannot be held in memory simultaneously?
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