Work branch

README.md

@@ -14,6 +14,7 @@ List of supported Data Structures and Algorithms are :
 - [Aho Corasick](https://github.com/thsubaku9/string-dsa/blob/main/src/search/AhoCorasick.js)
 - [Bloom Filter](https://github.com/thsubaku9/string-dsa/blob/main/src/BloomFilter.js)
 - [Bracket Balance](https://github.com/thsubaku9/string-dsa/blob/main/src/bracketBalance.js)
+- [Burrows Wheeler Transform](https://github.com/thsubaku9/string-dsa/blob/main/src/suffix/BWT.js)
 - [Burst Sort](https://github.com/thsubaku9/string-dsa/blob/main/src/sort/burstSort.js)
 - [Custom Sort](https://github.com/thsubaku9/string-dsa/blob/main/src/sort/stringSort.js)
 - [Dice Coefficient](https://github.com/thsubaku9/string-dsa/blob/main/src/dice_coeff.js)
@@ -68,4 +69,4 @@ $ npm run coverage
 
 ## License
 
-[ISC](https://github.com/thsubaku9/string-dsa/blob/main/LICENSE)
+[GNU General Public License v3.0](https://github.com/thsubaku9/string-dsa/blob/main/LICENSE)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "string-dsa",
-  "version": "1.5.1",
+  "version": "2.0.0",
   "description": "String Data Structures and Algorithms Library in JavaScript",
   "main": "src/index.js",
   "files": [
@@ -23,6 +23,7 @@
     "String Data Structures",
     "Aho Corasick",
     "Bloom Filter",
+    "Burrows Wheeler Transform",
     "Custom Sort",
     "Levenshtein Distance",
     "Suffix Array",

src/index.js

@@ -5,14 +5,15 @@ const editDist = require('./edit_distance');
 const lcs = require('./lcs');
 const { AhoCorasick, kmp, rabinKarp } = require('./search');
 const { burstSort, customSort, sorted } = require('./sort');
-const { Suffix } = require('./suffix');
+const { BWT, Suffix } = require('./suffix');
 const Trie = require('./Trie');
 
 module.exports = {
   AhoCorasick,
   BloomFilter,
   bracketBalance,
   burstSort,
+  BWT,
   customSort,
   diceCoeff,
   editDist,

src/suffix/BWT.js

@@ -0,0 +1,50 @@
+const { sort } = require("../sort/stringSort");
+const Suffix = require("./SuffixMain");
+
+/**
+ * Burrows Wheeler Transformation
+ *
+ * @param {String} text the string that you wish to find BWT of
+ *
+ * @returns {String} the respective BWT of the string
+ */
+function transform(text) {
+  let mySfx = new Suffix(text);
+  let bwt_t = "";
+
+  let res = mySfx.suffixArray();
+
+  for (let i = 0; i < res.length; i++) {
+    bwt_t += mySfx.originalString[(res[i] + res.length - 1) % res.length];
+  }
+
+  return bwt_t;
+}
+
+/**
+ * inverse Burrows Wheeler Transformation
+ *
+ * @param {String} bwt_t the BWT representation of the string
+ *
+ * @returns {String} the original string
+ */
+function inverse_transform(bwt_t) {
+  let index_sort = sort(bwt_t.split(""), true);
+  let inverse_index_pos = new Array(bwt_t.length);
+  for (let i = 0; i < bwt_t.length; i++) inverse_index_pos[index_sort[i]] = i;
+
+  let start_pos = index_sort[0]; let end_pos = 0;
+  let text = bwt_t[start_pos];
+
+  while (end_pos != index_sort[0]) {
+    text = bwt_t[end_pos] + text;
+    start_pos = end_pos;
+    end_pos = inverse_index_pos[end_pos];
+  }
+  return text;
+}
+
+module.exports = {
+  transform,
+  inverse_transform,
+};

src/suffix/SuffixMain.js

@@ -125,7 +125,7 @@ class SuffixMain {
   }
 
   /**
-   * This function computes the suffixArray of the given string in linear time
+   * This function computes the suffixArray of the given string
    *
    * @returns {Array} indexed based suffix array
    */

src/suffix/index.js

@@ -1,5 +1,7 @@
 const Suffix = require("./SuffixMain");
+const BWT = require("./BWT");
 
 module.exports = {
+  BWT,
   Suffix,
 };

test/suffix/test_BWT.js

@@ -0,0 +1,23 @@
+const assert = require("assert");
+const BWT = require("../../src").BWT
+describe("BWT tests", () =>{
+
+    const st1 = "candy" , st2 = "banana"
+    const bwt1 = "yc$nad", bwt2 = "annb$aa"
+    const inv1 = `${st1}$`, inv2 = `${st2}$`
+    it("should find the correct BWT", () =>{
+        const res1 = BWT.transform(st1)
+        const res2 = BWT.transform(st2)
+
+        assert.deepStrictEqual(res1, bwt1);
+        assert.deepStrictEqual(res2, bwt2);
+    })
+
+    it("should find the correct iBWT", () =>{
+        const res1 = BWT.inverse_transform(bwt1)
+        const res2 = BWT.inverse_transform(bwt2)
+
+        assert.deepStrictEqual(res1,inv1);
+        assert.deepStrictEqual(res2,inv2);
+    })
+})