Java code explainers

import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;

public class UnionFind {
    private final int[] parent;
    private final int[] rank;
    private int count;

import java.util.*;
 
public class TopologicalSort {
 

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
 

import java.util.Arrays;
 
public class SlidingWindow {
    // Returns the maximum sum of any contiguous subarray of length k.

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;

public final class Quicksort {
 
    private Quicksort() {
    }