Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>
void swap(int *a, int *b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}
void sort(int arr[], int n)
{
    for (int i = 0; i < n - 1; i++)
    {
        for (int j = i + 1; j < n; j++)
        {
            if (arr[i] > arr[j])
            {
                swap(&arr[i], &arr[j]);
            }
        }
    }
}
int find_duplicate(int arr[], int n) {
    for(int i = 0; i < n; i++){
        if(arr[i] == arr[i + 1]){
            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]);
    sort(arr, n);
    int result = find_duplicate(arr, n);
    printf("%d", result);
    return 0;
}   

Solving Approach