Find Duplicate in Range 0 and n-1

#include <stdio.h>
#include <stdlib.h>

int find_duplicate(int arr[], int n) {
    // Time: O(n). Space: O(1)
    if (n == 0) {
        // Invalid input. Return -1
        return -1;
    }
    int sum = arr[0];
    int min = arr[0];
    int max = arr[0];
    for (int i = 1; i < n; i++) {
        if (arr[i] < min) {
            min = arr[i];
        }
        if (arr[i] > max) {
            max = arr[i];
        }
        sum += arr[i];
    }
    int non_dup_sum = (min + max) * (max - min + 1) / 2;

    return abs(sum - non_dup_sum);
}

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;
}