Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    int freq[100] = {0};
    int i = 0;
    while (freq[arr[i]] == 0)
    {        
        freq[arr[i]]++;
        i++;
    }
    if (i == n )
        return -1;
    else 
        return arr[i];
}

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