Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
        for (int i = 0; i < n; i++){
            for (int j = i+1; j< n; j++){
                if(arr[i] == arr[j]){
                    return arr[i];
                }
            }
        }
        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