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19.KMP.cpp

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+/*
+ * This program takes a text and a pattern and searches the pattern inside the text
+ * using Knuth- Morris- Pratt Algorithm
+ *
+ *      Coded by: Abdurrezak Efe
+ *
+ * */
+#include <iostream>
+
+using namespace std;
+
+int fail[10000]; //assuming pattern has a length less than or equal to 10000
+
+void failure(string s)
+{
+    int i=1;
+    int j=0;
+    while(i<s.size())
+    {
+        if(s[i] == s[j])
+            fail[i] = j+1, i++, j++;
+        else if(j>0)
+            j =  fail[j-1];
+        else
+            fail[i] = 0, i++;
+    }
+}
+
+int kmp(string text, string pattern)
+{
+    int i=0;
+    int j=0;
+    while(i<text.size())
+    {
+        if(text[i] == pattern[j])
+            if(j == pattern.size()-1)
+                return i-j; // we have a match
+            else
+                i++,j++;
+        else
+            if(j>0)
+                j = fail[j-1];
+            else
+                i++;
+    }
+    return -1;
+
+}
+
+int main()
+{
+    string text, pattern;
+    cin >> text >> pattern;
+
+    cout << kmp(text, pattern) << endl;
+}