[hihoCoder] Trie树

This is a application of the Trie data structure, with minor extension. The critical part in this problem is to count all the words that have a particualr prefix and the problem has given nice hints to make this extension.

Two functions require to be implemented: add a word to the Trie and search the Trie for all words with a particular prefix.

The code is as follows.

If you are not familiar with Trie, you may refer to this solution first to get the basic idea of it.

#include <iostream>

using namespace std;

class TrieNode {
public:
int count;
TrieNode* children[26];
TrieNode() {
count = 0;
for (int i = 0; i < 26; i++)
children[i] = NULL;
}
};

class Dictionary {
public:
Dictionary() {
root = new TrieNode();
}

void insert(char* word) {
TrieNode* run = root;
for (int i = 0; word[i]; i++) {
if (!(run -> children[word[i] - 'a']))
run -> children[word[i] - 'a'] = new TrieNode();
run = run -> children[word[i] - 'a'];
run -> count++;
}
}

int search(char* prefix) {
TrieNode* run = root;
for (int i = 0; prefix[i]; i++) {
if (run)
run = run -> children[prefix[i] - 'a'];
else break;
}
if (!run) return false;
return run -> count;
}

private:
TrieNode* root;
};

int main(void) {
int dictSize;
while (scanf("%d", &dictSize) != EOF) {
Dictionary dictionary;
char word[20];
for (int i = 0; i < dictSize; i++) {
scanf("%s", word);
dictionary.insert(word);
}
int querySize;
scanf("%d", &querySize);
char prefix[20];
for (int i = 0; i < querySize; i++) {
scanf("%s", prefix);
printf("%d\n", dictionary.search(prefix));
}
}
return 0;
}