Aho-corasick algorithm for pattern matching in cpp.

Aho-corasick.cpp

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+using namespace std;
+#include <bits/stdc++.h>
+
+const int MAXS = 500;
+
+const int MAXC = 26;
+
+int out[MAXS];
+
+int f[MAXS];
+
+int g[MAXS][MAXC];
+
+int buildMatchingMachine(string arr[], int k)
+{
+    memset(out, 0, sizeof out);
+
+    memset(g, -1, sizeof g);
+
+    int states = 1;
+
+    for (int i = 0; i < k; ++i)
+    {
+        const string &word = arr[i];
+        int currentState = 0;
+
+        for (int j = 0; j < word.size(); ++j)
+        {
+            int ch = word[j] - 'a';
+
+            if (g[currentState][ch] == -1)
+                g[currentState][ch] = states++;
+
+            currentState = g[currentState][ch];
+        }
+
+        out[currentState] |= (1 << i);
+    }
+
+    for (int ch = 0; ch < MAXC; ++ch)
+        if (g[0][ch] == -1)
+            g[0][ch] = 0;
+
+    memset(f, -1, sizeof f);
+
+    queue<int> q;
+
+    for (int ch = 0; ch < MAXC; ++ch)
+    {
+
+        if (g[0][ch] != 0)
+        {
+            f[g[0][ch]] = 0;
+            q.push(g[0][ch]);
+        }
+    }
+
+    while (q.size())
+    {
+        int state = q.front();
+        q.pop();
+
+        for (int ch = 0; ch <= MAXC; ++ch)
+        {
+
+            if (g[state][ch] != -1)
+            {
+                int failure = f[state];
+
+                while (g[failure][ch] == -1)
+                    failure = f[failure];
+
+                failure = g[failure][ch];
+                f[g[state][ch]] = failure;
+
+                out[g[state][ch]] |= out[failure];
+
+                q.push(g[state][ch]);
+            }
+        }
+    }
+
+    return states;
+}
+
+int findNextState(int currentState, char nextInput)
+{
+    int answer = currentState;
+    int ch = nextInput - 'a';
+
+    while (g[answer][ch] == -1)
+        answer = f[answer];
+
+    return g[answer][ch];
+}
+
+void searchWords(string arr[], int k, string text)
+{
+    buildMatchingMachine(arr, k);
+
+    int currentState = 0;
+
+    for (int i = 0; i < text.size(); ++i)
+    {
+        currentState = findNextState(currentState, text[i]);
+
+        if (out[currentState] == 0)
+            continue;
+
+        for (int j = 0; j < k; ++j)
+        {
+            if (out[currentState] & (1 << j))
+            {
+                cout << "Word " << arr[j] << " appears from "
+                     << i - arr[j].size() + 1 << " to " << i << endl;
+            }
+        }
+    }
+}
+
+int main()
+{
+    string arr[] = {"he", "she", "hers", "his"};
+    string text = "ahishers";
+    int k = sizeof(arr) / sizeof(arr[0]);
+
+    searchWords(arr, k, text);
+
+    return 0;
+}