// C implementation of search and insert operations on Trie
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define ARRAY_SIZE(a) sizeof(a)/sizeof(a[0])
// Alphabet size (# of symbols)
#define ALPHABET_SIZE (26)
// Converts key current character into index
// use only 'a' through 'z' and lower case
#define CHAR_TO_INDEX(c) ((int)c - (int)'a')
// trie node
struct TrieNode
{
struct TrieNode *children[ALPHABET_SIZE];
// isEndOfWord is true if the node represents
// end of a word
bool isEndOfWord;
};
// Returns new trie node (initialized to NULLs)
struct TrieNode *getNode(void)
{
struct TrieNode *pNode = NULL;
pNode = (struct TrieNode *)malloc(sizeof(struct TrieNode));
if (pNode)
{
int i;
pNode->isEndOfWord = false;
for (i = 0; i < ALPHABET_SIZE; i++)
pNode->children[i] = NULL;
}
return pNode;
}
// If not present, inserts key into trie
// If the key is prefix of trie node, just marks leaf node
void insert(struct TrieNode *root, const char *key)
{
int level;
int length = strlen(key);
int index;
struct TrieNode *pCrawl = root;
for (level = 0; level < length; level++)
{
index = CHAR_TO_INDEX(key[level]);
if (!pCrawl->children[index])
pCrawl->children[index] = getNode();
pCrawl = pCrawl->children[index];
}
// mark last node as leaf
pCrawl->isEndOfWord = true;
}
// Returns true if key presents in trie, else false
bool search(struct TrieNode *root, const char *key)
{
int level;
int length = strlen(key);
int index;
struct TrieNode *pCrawl = root;
for (level = 0; level < length; level++)
{
index = CHAR_TO_INDEX(key[level]);
if (!pCrawl->children[index])
return false;
pCrawl = pCrawl->children[index];
}
return (pCrawl->isEndOfWord);
}
// Driver
int main()
{
// Input keys (use only 'a' through 'z' and lower case)
char keys[][8] = {"the", "a", "there", "answer", "any",
"by", "bye", "their"};
char output[][32] = {"Not present in trie", "Present in trie"};
struct TrieNode *root = getNode();
// Construct trie
int i;
for (i = 0; i < ARRAY_SIZE(keys); i++)
insert(root, keys[i]);
// Search for different keys
printf("%s --- %s\n", "the", output[search(root, "the")] );
printf("%s --- %s\n", "these", output[search(root, "these")] );
printf("%s --- %s\n", "their", output[search(root, "their")] );
printf("%s --- %s\n", "thaw", output[search(root, "thaw")] );
return 0;
}
