Cracking the Coding Interview - Fooo

Solutions to Chapter 19 | Moderate
19 8 Design a method to find the frequency of occurrences of any given word in a book
SOLUTION
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The first question – which you should ask your interviewer – is if you’re just asking for a
single word (“single query”) or if you might, eventually, use the same method for many different
words (“repetitive queries”)? That is, are you simply asking for the frequency of “dog”,
or might you ask for “dog,” and then “cat,” “mouse,” etc?
Solution: Single Query
In this case, we simply go through the book, word by word, and count the number of times
that a word appears This will take O(n) time We know we can’t do better than that, as we
must look at every word in the book
Solution: Repetitive Queries
In this case, we create a hash table which maps from a word to a frequency Our code is then
like this:
1 Hashtable setupDictionary(String[] book) {
2 Hashtable table =
3 new Hashtable();
4 for (String word : book) {
5 word = word.toLowerCase();
6 if (word.trim() != “”) {
7 if (!table.containsKey(word)) table.put(word, 0);
8 table.put(word, table.get(word) + 1);
9 }
10 }
11 return table;
12 }
13
14 int getFrequency(Hashtable table, String word) {
15 if (table == null || word == null) return -1;
16 word = word.toLowerCase();
17 if (table.containsKey(word)) {
18 return table.get(word);
19 }
20 return 0;
21 }
Note: a problem like this is relatively easy. Thus, the interviewer is going to be
looking heavily at how careful you are. Did you check for error conditions?
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