Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    int max=0;
    for(int i=0;i<n;i++){
        if(arr[i]>max){
            max=arr[i];
        }
    }

    int freq[max+1];
    int j=max+1;
    for(int i=0;i<j;i++){
        freq[i]=0;
    }

    for(int i=0;i<n;i++){
        freq[arr[i]]++;
    }
    int o=0;
    for(int i=0;i<j;i++){
        if(freq[i]>1){
            o=i;
        }
    }
    return o;
}

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