Top K Frequent Words Solution Amazon OA 2021

Top K Frequent Words Solution

Given a non-empty list of words, return the k most frequent elements. Your answer should be sorted by frequency from highest to lowest. If two words have the same frequency, then the word with the lower alphabetical order comes first.

See Also : Amazon Online Assessment Questions 2021 Preparation

Example 1:

Input: ["i", "love", "leetcode", "i", "love", "coding"], k = 2
Output: ["i", "love"]
Explanation: "i" and "love" are the two most frequent words.
    Note that "i" comes before "love" due to a lower alphabetical order.

Example 2:

Input: ["the", "day", "is", "sunny", "the", "the", "the", "sunny", "is", "is"], k = 4
Output: ["the", "is", "sunny", "day"]
Explanation: "the", "is", "sunny" and "day" are the four most frequent words,
    with the number of occurrence being 4, 3, 2 and 1 respectively.

Note:

1. You may assume k is always valid, 1 ≤ k ≤ number of unique elements.
2. Input words contain only lowercase letters.

Follow up:

1. Try to solve it in O(n log k) time and O(n) extra space.

Solution

Program C++

static bool mycmp(pair<string,int> a,pair<string,int>b){
        if(a.second==b.second){
            return a.first<b.first;
        }
        return a.second>b.second;
    }
    vector<string> topKFrequent(vector<string>& words, int k) {
        map<string,int> mp;
        for(auto x:words){
            mp[x]++;
        }
        vector<pair<string,int>> ans(mp.begin(),mp.end());
        sort(ans.begin(),ans.end(),mycmp);
        vector<string> res;
        int i=0;
        while(k--){
            res.push_back(ans[i].first);
            i++;
        }
        return res;
    }

Program Java

class Solution {
public List topKFrequent(String[] words, int k) {

    if (words == null || words.length == 0) {
        return Collections.emptyList();
    }
    
    Map<String, Integer> wordMap = new HashMap<>();
    
    for (String word : words) {
        int count =  wordMap.get(word) == null ? 0 : wordMap.get(word);
        wordMap.put(word, ++count);
    }
    
    PriorityQueue<PElement> pq = new PriorityQueue<>(new PElementComparator());
    
    for (Map.Entry<String, Integer> entry : wordMap.entrySet()) {
        PElement p = new PElement(entry.getKey(), entry.getValue());
        pq.add(p);
    }
    
    List<String> result = new ArrayList<>(); 
    for (int i = 0; i < k; i++) {
        PElement element = pq.poll();
        result.add(element.word);
    }
    
    return result;
}

private static class PElement {
    String word;
    int count;
    
    public PElement(String word, int count) {
        this.word = word;
        this.count = count;
    }
    
    public String getWord() {
        return word;
    }
    public int getCount() {
        return count;
    }
}

private static class PElementComparator implements Comparator<PElement> {
    public int compare(PElement p1, PElement p2) {
        if (p1 == p2) {
            return 0;
        }
        if (p1.getCount() > p2.getCount()) {
            return -1;
        }
        if (p2.getCount() > p1.getCount()) {
            return 1;
        } 
        return p1.getWord().compareTo(p2.getWord()); 
    }
}   
}

Program Python

import heapq
class OppositeString:
    def __init__(self, word):
        self.word = word
    def __lt__(self, other):
        return self.word > other.word
    def __eq__(self, other):
        return self.word == other.word
            
class Solution:
    def topKFrequent(self, words: List[str], k: int) -> List[str]:                
        wordsDict = Counter(words)
        heap = []
        heapify(heap)
        
        for w in wordsDict:
            heappush(heap, (wordsDict[w], OppositeString(w)))
            if len(heap) > k:
                heappop(heap)
        
        ans = ['']*k
        for i in range(k-1, -1, -1):
            ans[i] = heappop(heap)[1].word
            
        return ans

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