stringzy/dist/analyzing/patternCount.js

A versatile string manipulation library providing a range of text utilities for JavaScript and Node.js applications.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.patternCount = patternCount;
/**
 * Calculates the number of times a specific pattern occurs in a given text, including overlapping occurrences
 *
 * The algorithm used here is based on the Knuth-Morris-Pratt (KMP) pattern matching algorithm for better performance
 *
 * @param {string} text - The text for which we want to count the occurrences of a specific pattern.
 * @param {string} pattern - The pattern to search for within the text.
 * @returns {number} - The number of times the pattern occurs in the text (overlapping).
 */
function patternCount(text, pattern) {
    if (pattern.length === 0) {
        return 0; // No pattern to search for
    }
    const prefixFunction = computePrefixFunction(pattern);
    let count = 0;
    let j = 0; // Index for pattern
    for (let i = 0; i < text.length; i++) {
        while (j > 0 && text[i] !== pattern[j]) {
            j = prefixFunction[j - 1];
        }
        if (text[i] === pattern[j]) {
            j++;
        }
        if (j === pattern.length) {
            count++;
            j = prefixFunction[j - 1]; // Allow for overlapping matches
        }
    }
    return count;
}
/**
 * Computes the prefix function (partial match table) for KMP algorithm.
 * @param {string} pattern - The pattern string.
 * @returns {number[]} - The prefix function array.
 */
function computePrefixFunction(pattern) {
    const prefixFunction = new Array(pattern.length).fill(0);
    let j = 0;
    for (let i = 1; i < pattern.length; i++) {
        while (j > 0 && pattern[i] !== pattern[j]) {
            j = prefixFunction[j - 1];
        }
        if (pattern[i] === pattern[j]) {
            j++;
        }
        prefixFunction[i] = j;
    }
    return prefixFunction;
}