Z algorithm

README.md

@@ -79,6 +79,8 @@ Various Math algorithms:
 Various String algorithms:
 
 - [Levenshtein Distance](https://github.com/manrajgrover/algorithms-js/blob/master/src/algorithms/string/levenshtein_distance.js)
+- [Z-Algorithm](https://github.com/manrajgrover/algorithms-js/blob/master/src/algorithms/string/zalgorithm.js)
+
 
 #### Geometry
 Various Geometry algorithms:

src/algorithms/string/index.js

@@ -1,5 +1,7 @@
 const levenshteindistance = require('./levenshtein_distance');
+const zalgorithm = require('./zalgorithm');
 
 module.exports = {
-  levenshteindistance
+  levenshteindistance,
+  zalgorithm
 };

src/algorithms/string/zalgorithm.js

@@ -0,0 +1,51 @@
+/**
+ * @param {string} text
+ * @param {string} pattern
+ * @return {Array.<Number>|null}    returns a list of index which is the begginning of the pattern
+*/
+const zAlgorithm = (text, pattern) => {
+  if (!text || !pattern) { return null; }
+
+  const str = pattern + '$' + text;
+  const z = new Array(str.length).fill(0);
+
+  let l = 0;
+  let r = 1;
+  let k = 0;
+
+  for (let i = 0; i < z.length; i++) {
+    if (i > r) {
+      l = r = i;
+      while (r < z.length && str[r-l] === str[r]) {
+        r++;
+      }
+      z[i] = r-l;
+      r--;
+    }
+    else {
+      k = i-l;
+      if (z[k] < r-i+1) {
+        z[i] = z[k];
+      }
+      else {
+        l = i;
+        while (r < z.length && str[r-l] === str[r]) {
+          r++;
+        }
+        z[i] = r-l;
+        r--;
+      }
+    }
+  }
+
+  let ret = [];
+  for (let i = 0; i < z.length; i++) {
+    if (z[i] >= pattern.length) {
+      ret.push(i - pattern.length - 1);
+    }
+  }
+
+  return ret;
+};
+
+module.exports = zAlgorithm;

test/algorithms/string/testZAlgorithm.js

@@ -0,0 +1,53 @@
+/* eslint-env mocha */
+const zalgorithm = require('../../../src').algorithms.string.zalgorithm;
+const assert = require('assert');
+
+describe('Z Algorithm', () => {
+  it('should return [4]', () => {
+    const text = 'xaayaab';
+    const pattern = 'aab';
+
+    const result = zalgorithm(text, pattern);
+    assert.deepEqual(result, [4]);
+  });
+
+  it('should return [0,5,9]', () => {
+    const text = 'aabxcaabxaabxay';
+    const pattern = 'aabx';
+
+    const result = zalgorithm(text, pattern);
+    assert.deepEqual(result, [0,5,9]);
+  });
+
+  it('should return [6]', () => {
+    const text = 'abxabcabcaby';
+    const pattern = 'abcaby';
+
+    const result = zalgorithm(text, pattern);
+    assert.deepEqual(result, [6]);
+  });
+
+  it('should return null when text or pattern is empty', () => {
+    const text = '';
+    const pattern = '';
+
+    const result = zalgorithm(text, pattern);
+    assert.deepEqual(result, null);
+  });
+
+  it('should return [0,54]', () => {
+    const text = 'Mississippi is a beautiful state with lots of rivers. Mississippi River is the longest river in the United States.';
+    const pattern = 'Mississippi';
+
+    const result = zalgorithm(text, pattern);
+    assert.deepEqual(result, [0,54]);
+  });
+
+  it('should return [6,194]', () => {
+    const text = 'Mount Everest, also known as Sagarmatha in Nepal, is the world\'s tallest mountain. It is a part of the Himalayas and has long been a challenge for climbers. The first successful ascent of Mount Everest was in 1953 by Sir Edmund Hillary and Tenzing Norgay.';
+    const pattern = 'Everest';
+
+    const result = zalgorithm(text, pattern);
+    assert.deepEqual(result, [6,194]);
+  });
+});