🚧 progress: First draft.

Author: make-github-pseudonymous-again

README.md

@@ -4,12 +4,12 @@
 Longest prefix/suffix array for JavaScript.
 See [docs](https://string-data-structure.github.io/longest-prefix-suffix-array/index.html).
 
-> :building_construction: Caveat emptor! This is work in progress. Code may be
-> working. Documentation may be present. Coherence may be. Maybe.
-
-> :warning: Depending on your environment, the code may require
-> `regeneratorRuntime` to be defined, for instance by importing
-> [regenerator-runtime/runtime](https://www.npmjs.com/package/regenerator-runtime).
+```js
+import {build} from '@string-data-structure/longest-prefix-suffix-array';
+const s = 'abracadabra';
+const t = new Int32Array(s.length + 1);
+build(s, 0, s.length, t, 0);
+```
 
 [![License](https://img.shields.io/github/license/string-data-structure/longest-prefix-suffix-array.svg)](https://raw.githubusercontent.com/string-data-structure/longest-prefix-suffix-array/main/LICENSE)
 [![Version](https://img.shields.io/npm/v/@string-data-structure/longest-prefix-suffix-array.svg)](https://www.npmjs.org/package/@string-data-structure/longest-prefix-suffix-array)

doc/manual/usage.md

@@ -1,19 +1,8 @@
 # Usage
 
-> :warning: Depending on your environment, the code may require
-> `regeneratorRuntime` to be defined, for instance by importing
-> [regenerator-runtime/runtime](https://www.npmjs.com/package/regenerator-runtime).
-
-First, require the polyfill at the entry point of your application
-```js
-require( 'regenerator-runtime/runtime' ) ;
-// or
-import 'regenerator-runtime/runtime.js' ;
-```
-
-Then, import the library where needed
+Import the library where needed
 ```js
-const longestPrefixSuffixArray = require( '@string-data-structure/longest-prefix-suffix-array' ) ;
+const {build} = require( '@string-data-structure/longest-prefix-suffix-array' ) ;
 // or
-import * as longestPrefixSuffixArray from '@string-data-structure/longest-prefix-suffix-array' ;
+import {build} from '@string-data-structure/longest-prefix-suffix-array' ;
 ```

src/build.js

@@ -0,0 +1,21 @@
+/**
+ * Computes for each j the largest 0 <= i < j such that
+ * p.slice(0, i) is p.slice(j-i, j).
+ *
+ * @param {ArrayLike} p
+ * @param {number} pi
+ * @param {number} pj
+ * @param {number[]} t
+ * @param {number} ti
+ */
+const build = (p, pi, pj, t, ti) => {
+	t[ti] = -1;
+	let si = ti;
+	let m = -1;
+	for (let i = pi; i < pj; ++i) {
+		while (m >= 0 && p[i] !== p[pi + m]) m = t[ti + m];
+		t[++si] = ++m;
+	}
+};
+
+export default build;

src/index.js

@@ -1,2 +1 @@
-const answer = 42;
-export default answer;
+export {default as build} from './build.js';

test/src/_fixtures.js

@@ -0,0 +1,10 @@
+import {build} from '../../src/index.js';
+
+const _lpsa = (p, pi, pj) => {
+	// eslint-disable-next-line unicorn/no-new-array
+	const t = new Array(pj - pi + 1);
+	build(p, pi, pj, t, 0);
+	return t;
+};
+
+export const lpsa = (input) => _lpsa(input, 0, input.length);

test/src/api.js

@@ -0,0 +1,50 @@
+import test from 'ava';
+
+import {lpsa} from './_fixtures.js';
+
+const isLongestPrefixSuffixArray = (t, table, input) => {
+	t.is(table[0], -1);
+	for (let i = 1; i <= input.length; ++i) {
+		t.not(table[i], -1);
+		// Prefix and suffix match
+		t.is(input.slice(0, table[i]), input.slice(i - table[i], i));
+		if (table[i] + 1 < i) {
+			// A longer prefix/suffix pair does not match
+			t.not(input.slice(0, table[i] + 1), input.slice(i - (table[i] + 1), i));
+		}
+	}
+};
+
+const macro = (t, input, expected) => {
+	const table = lpsa(input);
+	t.deepEqual(table, expected);
+	isLongestPrefixSuffixArray(t, table, input);
+};
+
+macro.title = (title, input, expected) =>
+	title ?? `lpsa(${input}) is ${JSON.stringify(expected)}`;
+
+const auto = (t, input) => {
+	const table = lpsa(input);
+	isLongestPrefixSuffixArray(t, table, input);
+};
+
+auto.title = (title, input) =>
+	title ?? `isLongestPrefixSuffixArray(lpsa(${input}))`;
+
+test(macro, '', [-1]);
+test(macro, 'abcd', [-1, 0, 0, 0, 0]);
+test(macro, 'aaaa', [-1, 0, 1, 2, 3]);
+test(macro, 'axax', [-1, 0, 0, 1, 2]);
+test(macro, 'axxa', [-1, 0, 0, 0, 1]);
+test(macro, 'aaaab', [-1, 0, 1, 2, 3, 0]);
+test(macro, 'abcabcacab', [-1, 0, 0, 0, 1, 2, 3, 4, 0, 1, 2]);
+test(macro, 'abracadabra', [-1, 0, 0, 0, 1, 0, 1, 0, 1, 2, 3, 4]);
+test(
+	macro,
+	'abaababaabaababaababa',
+	[-1, 0, 0, 1, 1, 2, 3, 2, 3, 4, 5, 6, 4, 5, 6, 7, 8, 9, 10, 11, 7, 8],
+);
+
+test(auto, 'eifoiwhfeldkasjflkdshfldshflkkdadkkkkkkkkkkkkasjfdljfdleifo');
+test(auto, 'aaaaaaaaaaaabbbbbbbbbbaaaaaaaaabbbbbbbb');