Find Duplicate in Range 0 and n-1

Code

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

int cmp (const void*a,const void*b){
     return *(int*)a-*(int*)b;
}

int find_duplicate(int arr[], int n) {
    // Your logic here
    qsort(arr,n,sizeof(int),cmp);
    int prev=0;
    for (int i=1;i<n;i++){
        if (i==1){
            prev=arr[0];
        }

        if (arr[i]==prev) return arr[i];
        
        prev=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