Reverse an Array In-Place

Code

#include <stdio.h>

void reverse_array(int arr[], int n) {
    // Your logic here
    volatile int i = 0, j = n-1;
    while(i<j){
        arr[i] = arr[i] + arr[j];
        arr[j] = arr[i] - arr[j];
        arr[i] = arr[i] - arr[j];
        i++;j--;
    }

}

int main() {
    int n;
    scanf("%d", &n);

    int arr[100];
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    reverse_array(arr, n);

    for (int i = 0; i < n; i++) {
        printf("%d", arr[i]);
        if(i < n-1){
        	printf(" ");
        }
    }
    return 0;
}

Solving Approach

Use a two pointer approach, swap leftmost current index with rightmost current index.

For simplicity arr[i] = a, arr[j] = b

Swap:

• add both a+b and store into a

• subtract b from a to get the original value of a and store it in b

• subtract b from a to get the original value of b and store it in a