Posts

Showing posts from July, 2017

A string hash problem

Image
Earlier this week I was looking through various software developer jobs and I came across this one by Fog Creek. They've posted the following interesting problem, which is the subject of this post.
Find a 9 letter string of characters that contains only letters from acdegilmnoprstuw such that the `hash(the_string)` is 945924806726376 if `hash` is defined by the following pseudo-code: Int64 hash (String s) { Int64 h = 7 String letters = "acdegilmnoprstuw" for (Int32 i = 0; i < s.length; i++) { h = (h * 37 + letters.indexOf(s[i])) } return h } I had no clue what to do when I first read this. In fact, my first attempt was to brute force my way through \({16}^{9}\sim 68\cdot {10}^9\) possibilities. Obviously we need a better method than that.
from typing import Optional from itertools import product alphabet = 'acdegilmnoprstuw' def hash(string: str) -> int: "&quo…

Setting up ath10k

This post is meant as a simple reminder of how to get WIFI working in the event that I have to reinstall Debian on my Lenovo Flex 5, which appears to be a newer firmware.

First, run mkdir -p /lib/firmware/ath10k to create the subdirectory ath10k if it doesn't already exist. Now copy the QCA6174 directory from this GitHub repo there and rename the files QCA6174/hw*/firmware-5.bin* to just firmware*.bin.

Now reboot, and whoala! WIFI works.

Unfortunately, there still appears to be a few fails while loading the firmware, which I'll have to look into at some point. But for now, this is a quick fix to get things moving.
$ sudo dmesg | grep ath10k [ 2.186725] ath10k_pci 0000:03:00.0: pci irq msi oper_irq_mode 2 irq_mode 0 reset_mode 0 [ 2.463755] ath10k_pci 0000:03:00.0: firmware: failed to load ath10k/pre-cal-pci-0000:03:00.0.bin (-2) [ 2.463756] ath10k_pci 0000:03:00.0: Direct firmware load for ath10k/pre-cal-pci-0000:03:00.0.bin failed with error -2 [ 2.463765] ath10k_…