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BKTree.cpp
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BKTree.cpp
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/*******************************************************************************
Spell Checker using BK-Tree
This program is an implementation of a spell checker for English text. The
spell checker incorporates a database of known words, which is built from a
simple word list. The Burkhard-Keller Tree (BK-Tree for short) organizes the
word list for efficient searching.
BK-Tree implementation is based of the description in this article:
http://blog.notdot.net/2007/4/Damn-Cool-Algorithms-Part-1-BK-Trees
OTHER RESOURCES:
https://en.wikipedia.org/wiki/Levenshtein_distance
http://people.cs.vt.edu/shaffer/Book/C++3elatest.pdf (pg. 215 Sec. 6.3.2)
https://www.safaribooksonline.com/library/view/c-cookbook/0596007612/ch04s13
Created by Kyle Bludworth on 11/30/15.
Copyright © 2015 Kyle Bludworth. All rights reserved.
*******************************************************************************/
#include "BKTree.h"
using std::cout;
using std::endl;
using std::string;
using std::basic_string;
using std::vector;
BKTree::BKTree() { root = NULL; }
BKTree::~BKTree() { delete root; }
Node* BKTree::createNode(string w, size_t d)
{
Node* node = new Node();
node->word = w;
node->distance = d;
node->leftChild = NULL;
node->rightSibling = NULL;
return node;
}
void BKTree::add(string w)
{
if (root == NULL)
{
root = createNode(w, -1);
return;
}
Node* curNode = root;
Node* child;
Node* newChild;
size_t dist;
while (1) {
dist = levenshteinDistance(curNode->word, w);
if (!dist)
return;
child = curNode->leftChild;
while (child)
{
if (child->distance == dist)
{
curNode = child;
break;
}
child = child->rightSibling;
}
if (!child)
{
newChild = createNode(w, dist);
newChild->rightSibling = curNode->leftChild;
curNode->leftChild = newChild;
break;
}
}
}
void BKTree::search(string w, int t)
{
vector<string> suggestions;
bool wordFound = false;
recursiveSearch(root, suggestions, w, t, wordFound);
printSuggestions(suggestions, wordFound);
}
void BKTree::recursiveSearch(Node* curNode, vector<string>& suggestions, string w,
size_t t, bool& wordFound)
{
size_t curDist = levenshteinDistance(curNode->word, w);
size_t minDist = curDist - t;
size_t maxDist = curDist + t;
if (!curDist) {
wordFound = true;
return;
}
if (curDist <= t)
suggestions.push_back(curNode->word);
Node* child = curNode->leftChild;
if (!child) return;
while (child)
{
if (inRange(child->distance, minDist, maxDist))
recursiveSearch(child, suggestions, w, t, wordFound);
child = child->rightSibling;
}
}
bool BKTree::inRange(size_t curDist, size_t minDist, size_t maxDist)
{
return (minDist <= curDist && curDist <= maxDist);
}
void BKTree::printSuggestions(vector<string>& suggestions, bool wordFound)
{
if (wordFound)
{
cout << "Word is spelled correctly." << endl;
}
else if (suggestions.empty())
{
cout << "No suggestions found." << endl;
}
else
{
cout << "Did you mean: ";
for (int i = 0; i < suggestions.size() - 1; i++)
{
cout << suggestions[i] << ", ";
}
cout << suggestions[suggestions.size() - 1] << "?" << endl;
}
}
//https://en.wikipedia.org/wiki/Levenshtein_distance
size_t BKTree::levenshteinDistance(string w1, string w2)
{
if (w1.length() == 0)
return w2.length();
if (w2.length() == 0)
return w1.length();
size_t n_w1 = w1.length();
size_t n_w2 = w2.length();
int cost;
int d[n_w1 + 1][n_w2 + 1];
for (int i = 0; i <= n_w1; i++)
d[i][0] = i;
for (int i = 0; i <= n_w2; i++)
d[0][i] = i;
for (int i = 1; i <= n_w1; i++)
{
for (int j = 1; j <= n_w2; j++)
{
cost = (w1[i - 1] == w2[j - 1]) ? 0 : 1;
d[i][j] = min(d[i - 1][j] + 1,
d[i][j - 1] + 1,
d[i - 1][j - 1] + cost);
}
}
return d[n_w1][n_w2];
}
int BKTree::min(int a, int b, int c)
{
int min = a;
if (b < min)
min = b;
if (c < min)
min = c;
return min;
}
void BKTree::cleanString(basic_string<char>& s)
{
for (basic_string<char>::iterator p = s.begin();
p != s.end(); ++p)
{
*p = tolower(*p);
}
}