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import java.util.*;
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// https://en.wikipedia.org/wiki/Aho–Corasick_algorithm
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public class AhoCorasick {
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static final int ALPHABET_SIZE = 26;
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Node[] nodes;
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int nodeCount;
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public static class Node {
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int parent;
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char charFromParent;
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int suffLink = -1;
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int[] children = new int[ALPHABET_SIZE];
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int[] transitions = new int[ALPHABET_SIZE];
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boolean leaf;
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{
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Arrays.fill(children, -1);
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Arrays.fill(transitions, -1);
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}
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}
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public AhoCorasick(int maxNodes) {
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nodes = new Node[maxNodes];
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// create root
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nodes[0] = new Node();
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nodes[0].suffLink = 0;
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nodes[0].parent = -1;
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nodeCount = 1;
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}
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public void addString(String s) {
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int cur = 0;
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for (char ch : s.toCharArray()) {
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int c = ch - 'a';
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if (nodes[cur].children[c] == -1) {
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nodes[nodeCount] = new Node();
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nodes[nodeCount].parent = cur;
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nodes[nodeCount].charFromParent = ch;
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nodes[cur].children[c] = nodeCount++;
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}
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cur = nodes[cur].children[c];
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}
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nodes[cur].leaf = true;
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}
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public int suffLink(int nodeIndex) {
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Node node = nodes[nodeIndex];
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if (node.suffLink == -1)
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node.suffLink = node.parent == 0 ? 0 : transition(suffLink(node.parent), node.charFromParent);
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return node.suffLink;
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}
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public int transition(int nodeIndex, char ch) {
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int c = ch - 'a';
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Node node = nodes[nodeIndex];
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if (node.transitions[c] == -1)
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node.transitions[c] = node.children[c] != -1 ? node.children[c] : (nodeIndex == 0 ? 0 : transition(suffLink(nodeIndex), ch));
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return node.transitions[c];
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}
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// Usage example
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public static void main(String[] args) {
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AhoCorasick ahoCorasick = new AhoCorasick(1000);
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ahoCorasick.addString("bc");
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ahoCorasick.addString("abc");
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String s = "tabcbc";
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int node = 0;
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List<Integer> positions = new ArrayList<>();
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for (int i = 0; i < s.length(); i++) {
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node = ahoCorasick.transition(node, s.charAt(i));
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if (ahoCorasick.nodes[node].leaf)
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positions.add(i);
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}
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System.out.println(positions);
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}
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}
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