Nhiệm vụ | Cấp 6 | bài 8

You are given an implementation of a red-black tree. But some methods are broken. Analyze the code and fix the errors. The main method is not tested. All of the modifiers are correct. Don't change variable or method names.

The first parameter is the file name: file1. file1 only contains Latin letters, spaces, punctuation, dashes, and carriage returns. Sort the letters alphabetically and display the first 5 unique letters on a single line without separators.

Today we'll analyze some functionality of social networks. How do social networks know who to suggest as friends you might know? This task is easily solved using graphs.