Reverse the array problem:

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You are given an array of integers arr[]. You have to reverse the given array.

Note: Modify the array in place.

Examples:

Input: arr = [1, 4, 3, 2, 6, 5]
Output: [5, 6, 2, 3, 4, 1]
Explanation: The elements of the array are [1, 4, 3, 2, 6, 5]. After reversing the array, the first element goes to the last position, the second element goes to the second last position and so on. Hence, the answer is [5, 6, 2, 3, 4, 1].
Input: arr = [4, 5, 2]
Output: [2, 5, 4]
Explanation: The elements of the array are [4, 5, 2]. The reversed array will be [2, 5, 4].
Input: arr = [1]
Output: [1]
Explanation: The array has only single element, hence the reversed array is same as the original.

Constraints:
1 ≤ arr.size() ≤ 105
0 ≤ arr[i] ≤ 105

C++ Solution

Method 1: Using two-pointer technique

#include <iostream>
#include <vector>
using namespace std;

void reverseArray(vector<int>& arr) {
    int start = 0, end = arr.size() - 1;
    while (start < end) {
        swap(arr[start], arr[end]);
        start++;
        end--;
    }
}

int main() {
    vector<int> arr = {1, 2, 3, 4, 5};
    reverseArray(arr);

    for (int x : arr) {
        cout << x << " ";
    }
    return 0;
}

Python Solution:

arr = [1, 2, 3, 4, 5]
arr = arr[::-1]
print(arr)

Method 2: Using two-pointer loop

arr = [1, 2, 3, 4, 5]
start, end = 0, len(arr) - 1

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

print(arr)

Java Solution:

Method 1: Two-pointer method

public class Main {
    public static void reverseArray(int[] arr) {
        int start = 0, end = arr.length - 1;

        while (start < end) {
            int temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;

            start++;
            end--;
        }
    }

    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5};
        
        reverseArray(arr);

        for (int x : arr) {
            System.out.print(x + " ");
        }
    }
}

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