59 lines
2.1 KiB
Java
59 lines
2.1 KiB
Java
package it.cavallium.strangedb.java.objects.lists;
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public class KMP {
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public static int KMP(CharSequence content, CharSequence stringToFind) {
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int[] failureTable = failureTable(stringToFind);
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int targetPointer = 0; // current char in target string
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int searchPointer = 0; // current char in search string
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while (searchPointer < content.length()) { // while there is more to search with, keep searching
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if (content.charAt(searchPointer) == stringToFind.charAt(targetPointer)) { // case 1
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// found current char in targetPointer in search string
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targetPointer++;
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if (targetPointer == stringToFind.length()) { // found all characters
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int x = stringToFind.length() + 1;
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return searchPointer - x; // return starting index of found target inside searched string
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}
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searchPointer++; // move forward if not found target string
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} else if (targetPointer > 0) { // case 2
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// use failureTable to use pointer pointed at nearest location of usable string prefix
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targetPointer = failureTable[targetPointer];
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} else { // case 3
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// targetPointer is pointing at state 0, so restart search with current searchPointer index
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searchPointer++;
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}
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}
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return -1;
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}
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/**
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* Returns an int[] that points to last valid string prefix, given target string
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*/
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public static int[] failureTable(CharSequence target) {
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int[] table = new int[target.length() + 1];
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// state 0 and 1 are guarenteed be the prior
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table[0] = -1;
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table[1] = 0;
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// the pointers pointing at last failure and current satte
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int left = 0;
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int right = 2;
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while (right < table.length) { // RIGHT NEVER MOVES RIGHT UNTIL ASSIGNED A VALID POINTER
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if (target.charAt(right - 1) == target.charAt(left)) { // when both chars before left and right are equal, link both and move both forward
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left++;
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table[right] = left;
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right++;
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} else if (left > 0) { // if left isn't at the very beginning, then send left backward
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// by following the already set pointer to where it is pointing to
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left = table[left];
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} else { // left has fallen all the way back to the beginning
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table[right] = left;
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right++;
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}
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}
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return table;
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}
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}
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