Write a program to print top N trending hashtags

 You are given a set of hashtags and the number of times those have occured. 

Write a java program to print top N trending hashtags from the list of values.

Solution: The best suited data structure for figuring out top N elements is a heap - PriorityQueue is the java implementation for heap.

github: https://github.com/prasune/Algorithms/tree/master/src/main/java/com/test/algorithm/heap

package com.test.algorithm.heap;

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

public class TopNHashtags {

    public static void main(String[] args) {
        int n = 3;
        List<HashTagCount> hashTagList = new ArrayList<>();
        hashTagList.add(new HashTagCount("#sometag", 10));
        hashTagList.add(new HashTagCount("#sometag1", 1000));
        hashTagList.add(new HashTagCount("#sometag2", 900));
        hashTagList.add(new HashTagCount("#sometag3", 100));
        hashTagList.add(new HashTagCount("#sometag4", 50));
        hashTagList.add(new HashTagCount("#sometag", 10));

        printTopNTrendingHashTags(n, hashTagList);
    }

    private static void printTopNTrendingHashTags(int n, List<HashTagCount> hashTagList) {
        PriorityQueue<HashTagCount> topTrendingHashTags =
                new PriorityQueue<>(Comparator.comparing(HashTagCount::getCount).reversed());
        topTrendingHashTags.addAll(hashTagList);
        for (int i = 0; i< n; i++) {
            System.out.println(topTrendingHashTags.poll());
        }
    }
}

package com.test.algorithm.heap;

import java.util.Objects;

public class HashTagCount {

    private String hashTag;

    private long count;

    public HashTagCount(String hashTag, long count) {
        this.hashTag = hashTag;
        this.count = count;
    }

    public String getHashTag() {
        return hashTag;
    }

    public void setHashTag(String hashTag) {
        this.hashTag = hashTag;
    }

    public long getCount() {
        return count;
    }

    public void setCount(long count) {
        this.count = count;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        HashTagCount that = (HashTagCount) o;
        return hashTag.equals(that.hashTag);
    }

    @Override
    public int hashCode() {
        return Objects.hash(hashTag);
    }

    @Override
    public String toString() {
        return "TweetCount{" +
                "hashTag='" + hashTag + '\'' +
                ", count=" + count +
                '}';
    }
}