lgrthms/lib/algorithms/strings/knuthMorrisPratt.js

Algorithms and data structures for your JavaScript and TypeScript projects 🧑‍💻

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.knuthMorrisPratt = void 0;
// O(n + m) time | O(m) space — where
// n is the length of the string
// m is the length of the substring
function knuthMorrisPratt(string, substring) {
    const pattern = buildPattern(substring);
    let i = 0;
    let j = 0;
    while (i + substring.length - j <= string.length) {
        if (string[i] === substring[j]) {
            if (j === substring.length - 1) {
                return true;
            }
            i++;
            j++;
        }
        else if (j > 0) {
            j = pattern[j - 1] + 1;
        }
        else {
            i++;
        }
    }
    return false;
}
exports.knuthMorrisPratt = knuthMorrisPratt;
function buildPattern(substring) {
    const pattern = new Array(substring.length).fill(-1);
    let j = 0;
    let i = 1;
    while (i < substring.length) {
        if (substring[i] === substring[j]) {
            pattern[i] = j;
            i++;
            j++;
        }
        else if (j > 0) {
            j = pattern[j - 1] + 1;
        }
        else {
            i++;
        }
    }
    return pattern;
}