Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

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

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

Solving Approach