Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    int l = 0; 
    int r = 1;
    while(true)
    {
        if(arr[l] == arr[r])
        {
            return arr[l];
        }
        else
        {
            r++;
        }
        if(r >= n)
        {
            l++;
            r = l+1;
        }
    }
    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