Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    for(int i = 0; i < n; i++)
    {
        int flag = 0;
        for(int j = i + 1; j < n; j++)
        {
            if(arr[i] == arr[j])
            {
                flag = 1;
                break;
            }
        }
        if(flag)
        {
            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