PrintAllWordsTrie.cpp

// C implementation of search and insert operations
// on Trie
#include <iostream>
#include <stdlib.h>
#include <cstring>
using namespace std;

#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];

    // isLeaf is true if the node represents
    // end of a word
    bool isLeaf;
};

// 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->isLeaf = 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->isLeaf = 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 != NULL && pCrawl->isLeaf);
}

void print(TrieNode * root, string str){
    if (root->isLeaf)
        cout<<str<<endl;

    for (int index = 0; index < ALPHABET_SIZE; ++index) {

        TrieNode * pChild = root->children[index];
        if (pChild) {
            str.push_back('a'+index);
            print(pChild,str);
            str.pop_back();
        }
    }
}
void printUtil(TrieNode * root, string str){
    int len = str.length();
    TrieNode * node= root;
    for (int i = 0; i <len; ++i){
        node = node->children[str[i]-'a'];
    }
    print(node,str);
}

// 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]);
 string str = "an";
    printUtil(root, str);

    // 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;
}