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* refactor: change package * refactor: fix name --------- Co-authored-by: alxkm <alx@alx.com>
61 lines
1.6 KiB
Java
61 lines
1.6 KiB
Java
package com.thealgorithms.strings;
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/**
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* Implementation of Knuth–Morris–Pratt algorithm Usage: see the main function
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* for an example
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*/
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public final class KMP {
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private KMP() {
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}
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// a working example
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public static void main(String[] args) {
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final String haystack = "AAAAABAAABA"; // This is the full string
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final String needle = "AAAA"; // This is the substring that we want to find
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kmpMatcher(haystack, needle);
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}
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// find the starting index in string haystack[] that matches the search word P[]
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public static void kmpMatcher(final String haystack, final String needle) {
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final int m = haystack.length();
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final int n = needle.length();
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final int[] pi = computePrefixFunction(needle);
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int q = 0;
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for (int i = 0; i < m; i++) {
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while (q > 0 && haystack.charAt(i) != needle.charAt(q)) {
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q = pi[q - 1];
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}
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if (haystack.charAt(i) == needle.charAt(q)) {
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q++;
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}
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if (q == n) {
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System.out.println("Pattern starts: " + (i + 1 - n));
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q = pi[q - 1];
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}
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}
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}
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// return the prefix function
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private static int[] computePrefixFunction(final String p) {
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final int n = p.length();
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final int[] pi = new int[n];
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pi[0] = 0;
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int q = 0;
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for (int i = 1; i < n; i++) {
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while (q > 0 && p.charAt(q) != p.charAt(i)) {
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q = pi[q - 1];
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}
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if (p.charAt(q) == p.charAt(i)) {
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q++;
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}
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pi[i] = q;
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}
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return pi;
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}
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}
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