If you receive not_in_channel error when you use slack post message, you probably forgot to add your custom Slack app to the specific channel that you would like to receive notifications.

Click Integrations on channel settings and add your custom app.

Message Blocks

  • In order to use bold and strikethrough together, you need to use as follows:




WebP supports both lossy and lossless compression.

WebP lossless images are 26% smaller than PNG and WebP lossy images are 25–34% smaller than JPEG.

Con: older browser does not support.

In Next.js project, you can see the difference.


WebP with lossless compression




  • Image was not rendered after the deployment even though it works in the locally.

NFD(Normalization Form DeComposition)

  • Canonical Decomposition of all syllables and save them using the Korean alphabet code
  • Usage in Mac OS X

NFC(Normalization Form Composition)

  • Canonical Decomposition of all syllables followed by Canonical Composition
  • Usage in GNU/Linux system, usually in Windows




34. Find First and Last Position of Element in Sorted Array


Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

If target is not found in the array, return [-1, -1].

You must write an algorithm with O(log n) runtime complexity.

Example 1:

Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]

Example 2:

Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

Example 3:

Input: nums = [], target = 0
Output: [-1,-1]


  • 0 <= nums.length <= 105
  • -109 <= nums[i] <= 109
  • nums is a non-decreasing array.
  • -109 <= target <= 109




WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested

M1 is an arm64/v8 architecture, so that Docker will build an image with arm64/v8 architecture. In order to use Docker image in AWS EC2, which generally uses amazonlinux OS…