Top K Frequent Words

1
2
3
4
5
6

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.

1
2
3
4
5
6

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.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

class Solution {
    public List<String> topKFrequent(String[] words, int k) {
        Map<String, Integer> map = new HashMap<>();
        for (String word : words) {
            map.put(word, map.getOrDefault(word, 0) + 1);
        }
        PriorityQueue<String> queue = new PriorityQueue<>((a, b) -> {  
           Integer compare = Integer.compare(map.get(a), map.get(b));  
           if (compare != 0) {
               return -compare;
           } 
           return a.compareTo(b);
        });

        for (String word : map.keySet()) {
            queue.add(word);
        }
        List<String> result = new ArrayList<>();
        while (!queue.isEmpty() && k > 0) {
            result.add(queue.poll());
            k--;
        }
        return result;
    }  
}

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162

class Solution {
    Queue<int[]> q;
    Map<String, Integer> wordIndex = new HashMap<>();
    String[] words;
    int[][] heap;
    int n = 0;
    int k;
    public List<String> topKFrequent(String[] words, int k) {
        this.q = new PriorityQueue<int[]>((a, b) -> {
            return compare(a, b);
        });
        this.k = k;
        this.words = words;
        Map<Integer, Integer> freq = new HashMap<>();
        
        for (int i = 0; i < words.length; i++) {
            String word = words[i];
            Integer index = wordIndex.get(word);
            if (index == null) {
                index = i;
                wordIndex.put(word, index);
            } 
            
            freq.put(index, freq.getOrDefault(index, 0) + 1);
        }
        
        // System.out.println("freq: " + freq);
        // System.out.println("wordIndex: " + wordIndex);
        
        heap = new int[k + 1][];
        for (var entry: freq.entrySet()) {
            int[] word = new int[] { entry.getKey(), entry.getValue()};
            // System.out.println("word: " + Arrays.toString(word));
            add(word);
            // System.out.println("after : " + Arrays.deepToString(heap));
            // System.out.println("q : " + Arrays.deepToString(q.toArray()));
        }
        
        List<String> res = new ArrayList<>();
        while (size() > 0) {
            // System.out.println("min : " + Arrays.deepToString(heap));
            int[] max = poll();
            int index = max[0];
            res.add(0, words[index]);
        }
        
        return res;
    }
    
    void add(int[] word) {
        // if (n < k) {
        //     heap[++n] = word;
        //     swim(n);
        // } else {
        //     if (compare(word, heap[1]) > 0) {
        //         heap[1] = word;
        //         sink(n);
        //     }
        // }
        q.add(word);
        if (size() > k) {
            poll();
        }
    }
    
    // heap propery - min heap parent < child
    // change if parent > child; j > i
    void swim(int i) {
        int j = i / 2;
        if (j > 0 && compare(heap[i], heap[j]) < 0) {
            swap(i, j);
            swim(j);    
        }
    }
    
    int compare(int[] i, int[] j) {
        int c = Integer.compare(i[1], j[1]);
        if (c == 0) {
            c = - words[i[0]].compareTo(words[j[0]]);
        }
        // System.out.println("\tcompare " + compare + " " + i + " " + j);
        return c;
    }
    
    int[] poll() {
        // int[] max = heap[1];
        // heap[1] = heap[n--];
        // heap[n + 1][0] = -1;
        // heap[n + 1][1] = -1;
        // sink(1);
        // return max;
        return q.poll();
    }
    
    int size() {
        // return n;
        return q.size();
    }
    
    void sink(int i) {
        // System.out.println("\t" + Arrays.deepToString(heap));
        // System.out.println("\tsink " + i);
        int left = 2 * i;
        int right = 2 * i + 1;
        
        int smallest = i;
        if (left < heap.length && compare(heap[smallest], heap[left]) > 0) {
            smallest = left;
        }
        
        if (right < heap.length && compare(heap[smallest], heap[right]) > 0) {
            smallest = right;
        }
        
        if (i != smallest) {
            swap(i, smallest);
            sink(smallest);
        }
    }
    
    void swap(int i, int j) {
        var temp = heap[i];
        heap[i] = heap[j];
        heap[j] = temp;
    }
    
    
    public List<String> topKFrequent2(String[] words, int k) {
        Map<String, Integer> freq = new HashMap<>();
        for (String word: words) {
            freq.put(word, freq.getOrDefault(word, 0) + 1);
        }
        
        TreeSet<String>[] buckets = new TreeSet[words.length + 1];
        
        for (var entry: freq.entrySet()) {
            Integer i = entry.getValue();
            String word = entry.getKey();
            TreeSet<String> bucket = buckets[i];
            if (bucket == null) {
                bucket = new TreeSet<>();
            }
            bucket.add(word);
            buckets[i] = bucket;
        }
        System.out.println(Arrays.deepToString(buckets));
        List<String> res = new ArrayList<>();
        for (int i = buckets.length - 1; i >= 0 && res.size() < k; i--) {
            if (buckets[i] == null) {
                continue;
            }
            
            for (String word: buckets[i]) {
                if (res.size() == k) {
                    break;
                } 
                res.add(word);
            }
        }
        return res;
    }
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

class Solution {
    public List<String> topKFrequent(String[] words, int k) {
        Map<String, Integer> freq = new HashMap<>();
        for (String word: words) {
            freq.put(word, freq.getOrDefault(word, 0) + 1);
        }
        
        PriorityQueue<String> q = new PriorityQueue<>((a, b) -> {
           int c = freq.get(a).compareTo(freq.get(b));
            if (c != 0) return c;
            return - a.compareTo(b);
        });
        
        for (var e: freq.entrySet()) {
            q.add(e.getKey());
            if (q.size() > k) {
                q.poll();
            }
        }
        
        List<String> res = new ArrayList<>();
        
        while (q.size() > 0) {
            res.add(0, q.poll());
        }
        
        return res;
    }
}