Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    int freq[n] = {0};

    int count;
    for(int i = 0;i<n;i++){
        count = 1;
        for(int j=i+1;j<n;j++){
            if(arr[i] == arr[j]){
                count++;
                freq[j] = -1;
            }
        }
        if(freq[i] != -1){
            freq[i] = count;
        }
    }

    for(int i=0;i<n;i++){
        if(freq[i] == 2){
            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