Add Suffix Tree #45

Original file line number	Diff line number	Diff line change
Expand Up		@@ -34,6 +34,9 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
		- [Queue](src/_DataStructures_/Queue)
		- [Weave](src/_DataStructures_/Queue/weave)

	- [Suffix Tree](src/_DataStructures_/SuffixTree)


		### Logical Problems

		- [Anagrams](src/_Problems_/anagrams)
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121 changes: 121 additions & 0 deletions src/_DataStructures_/SuffixTree/index.js

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Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,121 @@
	/* eslint-disable no-plusplus */
	/*
	Implemented by watching this conceptually video: https://www.youtube.com/watch?v=VA9m_l6LpwI

	Suffix for banana are :
	banana
	anana
	nana
	ana
	na
	a

	Constructing a suffix tree is O(n*d) where d is length of max string

	Searching a suffix of a string is O(d) where d is length of suffix string.
	If found then return the index, else return -1

	*/

	class Node {
	constructor(value, isEnd, index) {
	this.data = value;
	this.isEnd = isEnd;
	this.index = index;
	this.next = new Map();
	}
	}

	class SuffixTree {
	constructor(string) {
	this.head = new Node();
	this.string = string;
	}

	constructSuffixTree() {
	const { string } = this;
	let currentString = '';
	for (let i = string.length - 1; i >= 0; i -= 1) {
	currentString = string[i] + currentString;
	let j = 0;
	let currentNode = this.head;
	while (j < currentString.length) {
	if (!currentNode.next.has(currentString[j])) {
	currentNode.next.set(currentString[j], new Node(currentString, true, i));
	break;
	} else {
	let k = 0;
	const partialMatchNode = currentNode.next.get(currentString[j]);
	const partialMatchString = partialMatchNode.data;

	let matchString = '';
	while (k < partialMatchString.length && j < currentString.length && partialMatchString[k] === currentString[j]) {
	matchString += currentString[j];
	k++;
	j++;
	}

	let diffString = '';
	while (k < partialMatchString.length) {
	diffString += partialMatchString[k];
	k++;
	}
	partialMatchNode.data = matchString;
	if (diffString) {
	partialMatchNode.next.set(diffString[0], new Node(diffString, true, partialMatchNode.index));
	partialMatchNode.isEnd = false;
	partialMatchNode.index = null;
	}

	if (partialMatchNode.next.has(currentString[j])) {
	currentNode = partialMatchNode;
	} else {
	let nextString = '';
	while (j < currentString.length) {
	nextString += currentString[j];
	j++;
	}
	partialMatchNode.next.set(nextString[0], new Node(nextString, true, i));
	break;
	}
	}
	}
	}
	}

	findSubstring(string) {
	if (!this.head.next.has(string[0])) {
	return -1;
	}

	let currentNode = this.head.next.get(string[0]);
	let currentNodeValue = currentNode.data;

	let i = 0; let j = 0;

	while (i < string.length) {
	j = 0;
	while (i < string.length && j < currentNodeValue.length && string[i++] === currentNodeValue[j++]);

	if (i === string.length && j === currentNodeValue.length && currentNode.isEnd) {
	return currentNode.index;
	}

	if (currentNode.next.has(string[i])) {
	currentNode = currentNode.next.get(string[i]);
	currentNodeValue = currentNode.data;
	} else {
	return -1;
	}
	}
	return -1;
	}
	}

	// const s = new SuffixTree('banana');
	// s.constructSuffixTree();

	// console.log(s.findSubstring('nana'));


	module.exports = SuffixTree;

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