Solution.py

class Solution:
    def minNumberOfSemesters(self, n: int, relations: List[List[int]], k: int) -> int:
        d = [0] * (n + 1)
        for x, y in relations:
            d[y] |= 1 << x
        q = deque([(0, 0)])
        vis = {0}
        while q:
            cur, t = q.popleft()
            if cur == (1 << (n + 1)) - 2:
                return t
            nxt = 0
            for i in range(1, n + 1):
                if (cur & d[i]) == d[i]:
                    nxt |= 1 << i
            nxt ^= cur
            if nxt.bit_count() <= k:
                if (nxt | cur) not in vis:
                    vis.add(nxt | cur)
                    q.append((nxt | cur, t + 1))
            else:
                x = nxt
                while nxt:
                    if nxt.bit_count() == k and (nxt | cur) not in vis:
                        vis.add(nxt | cur)
                        q.append((nxt | cur, t + 1))
                    nxt = (nxt - 1) & x