Code style fixes.

Author: trekhleb

README.md

@@ -72,7 +72,8 @@ a set of rules that precisely define a sequence of operations.
 * **Strings**
   * `A` [Levenshtein Distance](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/levenshtein-distance) - minimum edit distance between two sequences
   * `B` [Hamming Distance](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/hamming-distance) - number of positions at which the symbols are different
-  * `A` [Knuth–Morris–Pratt Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/knuth-morris-pratt) (KMP Algorithm) - substring search
+  * `A` [Knuth–Morris–Pratt Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/knuth-morris-pratt) (KMP Algorithm) - substring search (pattern matching)
+  * `A` [Z Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/z-algorithm) - substring search (pattern matching)
   * `A` [Rabin Karp Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/rabin-karp) - substring search
   * `A` [Longest Common Substring](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/longest-common-substring)
 * **Searches**

src/algorithms/string/z-algorithm/__test__/zAlgorithm.test.js

@@ -1,12 +1,16 @@
 import zAlgorithm from '../zAlgorithm';
 
 describe('zAlgorithm', () => {
-  it('should find word position in given text', () => {
-    expect(zAlgorithm('abcbcglx', 'abca')).toBe(-1);
-    expect(zAlgorithm('abcbcglx', 'bcgl')).toBe(3);
-    expect(zAlgorithm('abcxabcdabxabcdabcdabcy', 'abcdabcy')).toBe(15);
-    expect(zAlgorithm('abcxabcdabxabcdabcdabcy', 'abcdabca')).toBe(-1);
-    expect(zAlgorithm('abcxabcdabxaabcdabcabcdabcdabcy', 'abcdabca')).toBe(12);
-    expect(zAlgorithm('abcxabcdabxaabaabaaaabcdabcdabcy', 'aabaabaaa')).toBe(11);
+  it('should find word positions in given text', () => {
+    expect(zAlgorithm('abcbcglx', 'abca')).toEqual([]);
+    expect(zAlgorithm('abca', 'abca')).toEqual([0]);
+    expect(zAlgorithm('abca', 'abcadfd')).toEqual([]);
+    expect(zAlgorithm('abcbcglabcx', 'abc')).toEqual([0, 7]);
+    expect(zAlgorithm('abcbcglx', 'bcgl')).toEqual([3]);
+    expect(zAlgorithm('abcbcglx', 'cglx')).toEqual([4]);
+    expect(zAlgorithm('abcxabcdabxabcdabcdabcy', 'abcdabcy')).toEqual([15]);
+    expect(zAlgorithm('abcxabcdabxabcdabcdabcy', 'abcdabca')).toEqual([]);
+    expect(zAlgorithm('abcxabcdabxaabcdabcabcdabcdabcy', 'abcdabca')).toEqual([12]);
+    expect(zAlgorithm('abcxabcdabxaabaabaaaabcdabcdabcy', 'aabaabaaa')).toEqual([11]);
   });
 });

src/algorithms/string/z-algorithm/zAlgorithm.js

@@ -1,12 +1,13 @@
+// The string separator that is being used for "word" and "text" concatenation.
+const SEPARATOR = '$';
+
 /**
- * @param {string} word
- * @param {string} text
+ * @param {string} zString
  * @return {number[]}
  */
-
-function buildZArray(word, text) {
-  const zString = `${word}$${text}`;
+function buildZArray(zString) {
   const zArray = new Array(zString.length);
+
   let left = 0;
   let right = 0;
   let k = 0;
@@ -44,14 +45,32 @@ function buildZArray(word, text) {
 /**
  * @param {string} text
  * @param {string} word
- * @return {number}
+ * @return {number[]}
  */
 export default function zAlgorithm(text, word) {
-  const zArray = buildZArray(word, text);
-  for (let i = 1; i < zArray.length; i += 1) {
-    if (zArray[i] === word.length) {
-      return (i - word.length - 1);
+  // The list of word's positions in text. Word may be found in the same text
+  // in several different positions. Thus it is an array.
+  const wordPositions = [];
+
+  // Concatenate word and string. Word will be a prefix to a string.
+  const zString = `${word}${SEPARATOR}${text}`;
+
+  // Generate Z-array for concatenated string.
+  const zArray = buildZArray(zString);
+
+  // Based on Z-array properties each cell will tell us the length of the match between
+  // the string prefix and current sub-text. Thus we're may find all positions in zArray
+  // with the number that equals to the length of the word (zString prefix) and based on
+  // that positions we'll be able to calculate word positions in text.
+  for (let charIndex = 1; charIndex < zArray.length; charIndex += 1) {
+    if (zArray[charIndex] === word.length) {
+      // Since we did concatenation to form zString we need to subtract prefix
+      // and separator lengths.
+      const wordPosition = charIndex - word.length - SEPARATOR.length;
+      wordPositions.push(wordPosition);
     }
   }
-  return -1;
+
+  // Return the list of word positions.
+  return wordPositions;
 }