DS

while q:
    now = q[0]
    q.popleft()
    for i in range(0, (len(matrix[now]))):
        if (matrix[now][i] != 0):
            if used[i] == 0 or used[i] > used[now] + matrix[now][i]:
                q.append(i)
                used[i] = used[now] + matrix[now][i]