algorithm: ZFunction (TheAlgorithms#1239)

* algorithm: ZFunction * made requested changes * corrected spelling mistakes * made requested changes

Author: Adrito-M

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)
+ * @see https://cp-algorithms.com/string/z-function.html
+ * @param{String} text The string whose Z Function is to be calculated
+ * @return{Array} Returns an array whose i-th index is the value of Z Function for text at index i
+ */
+
+functionzFunction(text){
+constlength=text.length
+constzArray=Array(length).fill(0)
+// Initializing left and right variable to zero
+letleft=0
+letright=0
+for(letindex=0;index<length;index++){
+// If index is less than or equal to right, we reuse the values of zFunction at index right-index+1
+// It is made sure that value of zFunction at index is not greater than maximum possible value at index
+if(index<=right){
+zArray[index]=Math.min(right-index+1,zArray[index-left])
+}
+
+// After zArray[index] is initialized, we see if we can increase its value by trivially comparing character by character
+while(
+index+zArray[index]<length&&
+text[zArray[index]]===text[index+zArray[index]]
+){
+zArray[index]++
+}
+
+// If index + zArray[index] - 1 is greater than right, we update values of variables left and right
+if(index+zArray[index]-1>right){
+left=index
+right=index+zArray[index]-1
+}
+}
+returnzArray
+}
+
+exportdefaultzFunction

String/test/ZFunction.test.js

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+importzFunctionfrom'../ZFunction'
+
+test('Testing zFunction',()=>{
+expect(zFunction('aabxaayaab')).toEqual([10,1,0,0,2,1,0,3,1,0])
+expect(zFunction('aabxaabxcaabxaabxay')).toEqual([
+19,1,0,0,4,1,0,0,0,8,1,0,0,5,1,0,0,1,0
+])
+})