Autocomplete using Trie - c++

Question

I'm attempting to make some sort of autocomplete feature in c++. First by using a Trie and once that works (and most importantly, I know HOW it all works) I'll try it using a Ternary tree. But as for now I get a segmentation fault when ever I add words starting with a different characte than those already in the Trie.
Eg. we add "abc", "abcd" and "abcde" this is no problem. Later when I want to add (while the "abc" etc are still in the Trie) "xfce", "xfced" a segmentation fault occurs.
I've been debugging this for some while now and can't seem to find the problem.
I think the problem resides somewhere in Trie.cpp so that's the file I'll provide here. However it might be in the main function aswell but I don't wanna get yelled at for posting to much code...
#include "Trie.h"
#include <iostream>
Trie::Trie()
{
this->root = new Node(false);
}
Trie::~Trie()
{
}
Trie::Node::Node(bool isLeaf)
{
this->isLeaf = isLeaf;
}
void Trie::insert(const std::string& word)
{
Node* crawler = this->root;
int index;
for(int i = 0; i < word.length(); ++i)
{
index = CHAR_TO_INDEX(word.at(i));
if(!crawler->children[index])
{
crawler->children[index] = new Node(false);
}
crawler = crawler->children[index];
}
crawler->isLeaf = true;
}
int Trie::contains(const std::string& word)
{
int index;
Node* crawler = this->root;
for(int i = 0; i < word.length(); ++i)
{
index = CHAR_TO_INDEX(word.at(i));
if(!crawler->children[index])
{
return -1;
}
crawler = crawler->children[index];
}
return (crawler != NULL && crawler->isLeaf);
}
std::vector<std::string> Trie::possibleSuffixes(std::string& prefix)
{
Node* crawler = this->root;
int index;
std::vector<std::string> result;
for(int i = 0; i < prefix.length(); ++i)
{
index = CHAR_TO_INDEX(prefix.at(i));
crawler = crawler->children[index];
}
traverse(prefix, crawler, result);
return result;
}
void Trie::traverse(std::string prefix, Node* node, std::vector<std::string>& v)
{
if(node->isLeaf)
{
v.push_back(prefix);
}
for(int i = 0; i < ALPHABET; ++i)
{
if(node->children[i])
{
traverse(prefix + (char)('a' + i), node->children[i], v);
}
}
}
Entire Trie class:
#ifndef TRIE_H
#define TRIE_H
#include <string>
#include <vector>
#define ARRAYSIZE(a) sizeof(a / sizeof(a[0]))
#define ALPHABET 26
#define CHAR_TO_INDEX(c) ((int)c - (int)'a')
class Trie
{
private:
struct Node
{
Node(bool isLeaf);
struct Node *children[ALPHABET];
bool isLeaf;
};
Node *root;
void traverse(std::string prefix, Node* node, std::vector<std::string>& v);
public:
Trie();
~Trie();
int contains(const std::string& word); //Checks the existance of a specific word in the trie
void insert(const std::string& word); //Inserts new word in the trie if not already there
std::vector<std::string> possibleSuffixes(std::string& prefix);
};

Answer 1

Though you didn't mention about your Node class, I am assuming this -
class Node {
public:
bool isLeaf;
// must be >= 25 as you're inserting lowercase letters
// assuming your CHAR_TO_INDEX(ch) returns 0 based index
// e.g. 'a' => 0, 'b' => 1 ... 'z' => 25
Node* children[30];
// default constructor should be like this
Node(): isLeaf(false) {
for(int i = 0; i < 26; i++) {
children[i] = NULL;
}
}
~Node() {
for(int i = 0; i < 26; i++) {
if(children[i]) {
delete children[i];
children[i] = NULL;
}
}
delete this;
}
};
Please compare your Node class/struct whether its something like this.