Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    int count = 0,idx;
    for (int i=0;i<n;i++)
    {
        for (int j=i+1;j<n;j++)
        {
             if (arr[i] == arr[j])
            {
                count++;
                idx = arr[i];
            }
        }
    }
    if (count >= 1)
    {
        return idx;
    }
    else
    {
        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