Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    for (int i = 0; i < n; i++)
    {
        int index = (arr[i]>0)?arr[i]:-arr[i];
        if (arr[index]<0)
            return index;
        arr[index] = -arr[index];
    }
    return -1;
}

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

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

    int result = find_duplicate(arr, n);
    printf("%d", result);
    return 0;
}

Solving Approach