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GeezerVison is showing github.com — JavaScript/String/ZFunction.js at master · TheAlgorithms/JavaScript

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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
*/
function zFunction(text) {
const length = text.length
const zArray = Array(length).fill(0)
// Initializing left and right variable to zero
let left = 0
let right = 0
for (let index = 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
}
}
return zArray
}
export default zFunction
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