algorithm: ZFunction

String/ZFunction.js

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+/**
+ * Author: Adrito Mukherjee
+ * Implementation of ZFunction in JavaScript
+ * ZFunction at an index i gives the length of the longest substring starting at i, that is also a prefix of the whole string
+ * ZFunction for all indices in a string can be calculated in O(N)
+ * Explanation: https://cp-algorithms.com/string/z-function.html
+ */
+
+function ZFunction (text) {
+ const length = text.length
+ const ZArray = Array(length).fill(0)
+ let left = 0
+ let right = 0
+ for (let index = 0; index < length; index++) {
+ if (index <= right) {
+ ZArray[index] = Math.min(right - index + 1, ZArray[index - left])
+ }
+ while (
+ index + ZArray[index] < length &&
+ text[ZArray[index]] === text[index + ZArray[index]]
+ ) {
+ ZArray[index]++
+ }
+ if (index + ZArray[index] - 1 > right) {
+ left = index
+ right = index + ZArray[index] - 1
+ }
+ }
+ return ZArray
+}
+
+export default ZFunction

String/test/ZFunction.test.js

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+import ZFunction from '../ZFunction'
+
+test('Test Case 1', () => {
+ const text = 'aabxaayaab'
+ const ZArray = ZFunction(text)
+ expect(ZArray).toEqual([10, 1, 0, 0, 2, 1, 0, 3, 1, 0])
+})
+
+test('Test Case 2', () => {
+ const text = 'aabxaabxcaabxaabxay'
+ const ZArray = ZFunction(text)
+ expect(ZArray).toEqual([
+ 19, 1, 0, 0, 4, 1, 0, 0, 0, 8, 1, 0, 0, 5, 1, 0, 0, 1, 0
+ ])
+})