From a6251d329572eb8b34b3283fa975108a86bd58ed Mon Sep 17 00:00:00 2001
From: Bruno Freitas Tissei <bft15@inf.ufpr.br>
Date: Fri, 22 Nov 2019 01:14:00 -0300
Subject: [PATCH] Add Aho Corasick
Signed-off-by: Bruno Freitas Tissei <bft15@inf.ufpr.br>
---
algorithms/string/aho_corasick.cpp | 109 +++++++++++++++++++++++++++++
1 file changed, 109 insertions(+)
create mode 100644 algorithms/string/aho_corasick.cpp
diff --git a/algorithms/string/aho_corasick.cpp b/algorithms/string/aho_corasick.cpp
new file mode 100644
index 0000000..23f0302
--- /dev/null
+++ b/algorithms/string/aho_corasick.cpp
@@ -0,0 +1,109 @@
+/// Aho-Corasick
+///
+/// Time:
+/// - build: O(n)
+/// - preprocess: O(n)
+/// - match: O(p + n)
+/// - match_all: O(p + x)
+/// Space: O(n + p)
+///
+/// Caution:
+/// - Match might not find all occurences when repeated strings are given (fix with map)
+
+// *: Use only if "match_all" is necessary
+struct AhoCorasick {
+ struct Node {
+ //*: vector<int> words;
+ map<char,int> next;
+ int idx, fail, cnt, hei;
+
+ Node() : idx(-1), fail(0), cnt(0), hei(0) {}
+ int has(char i) { return next.count(i); }
+ int &operator[](char i) { return next[i]; }
+ };
+
+ vector<int> top;
+ vector<Node> trie;
+
+ AhoCorasick(const vector<string> &v) {
+ trie.pb(Node());
+ build(v);
+ top = preprocess();
+ }
+
+ int insert(const string &s) {
+ int n = 0;
+ for (int i = 0; i < s.size(); n = trie[n][s[i]], ++i)
+ if (!trie[n].has(s[i])) {
+ trie[n][s[i]] = trie.size();
+ //*: trie[n].hei = i + 1;
+ trie.pb(Node());
+ }
+ return n;
+ }
+
+ void build(const vector<string> &v) {
+ for (int i = 0; i < v.size(); ++i) {
+ int n = insert(v[i]);
+ trie[n].idx = i;
+ //*: trie[n].words.pb(i);
+ }
+ preprocess();
+ }
+
+ inline int suffix(int v, char c) {
+ while (v != 0 && !trie[v].has(c)) v = trie[v].fail;
+ if (trie[v].has(c)) v = trie[v][c];
+ return v;
+ }
+
+ vector<int> preprocess() {
+ vector<int> Q = { 0 };
+ for (int i = 0; i != Q.size(); ++i) {
+ int u = Q[i];
+ for (auto j : trie[u].next) {
+ trie[j.se].fail = u ? suffix(trie[u].fail, j.fi) : trie[u].fail;
+
+ //*: trie[j.se].words.insert(trie[j.se].words.end(),
+ // all(trie[trie[j.se].fail].words));
+ Q.pb(j.se);
+ }
+ }
+ return Q;
+ }
+
+ // Returns vector with indices of the strings occuring at
+ // least once in pattern p
+ vector<int> match(const string &p) {
+ int u = 0;
+ for (auto i : p) {
+ u = suffix(u, i);
+ trie[u].cnt++;
+ }
+
+ for (int i = top.size() - 1; i >= 0; --i)
+ trie[trie[top[i]].fail].cnt += trie[top[i]].cnt;
+
+ vector<int> ans;
+ for (auto i : trie)
+ if (i.idx != -1 && i.cnt)
+ ans.pb(i.idx);
+
+ sort(all(ans));
+ return ans;
+ }
+
+ // Returns all occurences of strings in p, where ans[i].fi
+ // is the indice of the string and ans[i].se is where in p
+ // does the string start
+ vector<ii> match_all(const string &p) {
+ int u = 0;
+ vector<ii> ans;
+ for (int i = 0; i < p.size(); ++i) {
+ u = suffix(u, p[i]);
+ for (auto j : trie[u].words)
+ ans.pb({j, i - trie[u].hei + 1});
+ }
+ return ans;
+ }
+};
--
GitLab