Python 3 solun using collections.Counter

from collections import Counter

def migratoryBirds(arr):
    return min([bird for bird, count in Counter(arr).items() if count == max(Counter(arr).values())])

overall time complexity is O(N)

Rust solution:

fn birds(arr: &[i32]) -> i32 {
    let mut map = HashMap::new();

    for &i in arr {
        *map.entry(i).or_insert(0) += 1;
    }

    *map.iter().max_by_key(|(&id, &n)| (n, -id)).unwrap().0
}

Python 1 liner: O(N)

return max(Counter(arr).items(), key= lambda i: 10*i[1] + 5-i[0])[0]

emp_arr = [0]*(max(arr)+1)
for i in arr:
    emp_arr[i] = emp_arr[i] + 1
for i in range(len(emp_arr)):
    if emp_arr[i] == max(emp_arr):
        return i

// couldn't find better 1 at the time

def migratoryBirds(arr):

n_arr = []
for i in set(arr):
    k = 0
    for j in arr:
        if i == j:
            k += 1
            n_arr.append((i, k))

m = max([i[1] for i in n_arr if i[1]])
return min([i[0] for i in n_arr if i[1] >= m])