From 2788923d72d0ba14868993f22aee92c0b223a261 Mon Sep 17 00:00:00 2001
From: Avigyan Das <abhigyan.smarajit@gmail.com>
Date: Sat, 12 Oct 2019 01:40:17 +0530
Subject: [PATCH] Z algorithm

---
 Algorithms/Z-algorithm/z-algorithm.cpp | 95 ++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 Algorithms/Z-algorithm/z-algorithm.cpp

diff --git a/Algorithms/Z-algorithm/z-algorithm.cpp b/Algorithms/Z-algorithm/z-algorithm.cpp
new file mode 100644
index 00000000..7f28f9c5
--- /dev/null
+++ b/Algorithms/Z-algorithm/z-algorithm.cpp
@@ -0,0 +1,95 @@
+// C++ implementation of Z algorithm
+//
+// Author: Avigyan Das
+
+
+// A C++ program that implements Z algorithm for pattern searching 
+#include<iostream> 
+using namespace std; 
+
+void getZarr(string str, int Z[]); 
+
+// prints all occurrences of pattern in text using Z algo 
+void search(string text, string pattern) 
+{ 
+	// Create concatenated string "P$T" 
+	string concat = pattern + "$" + text; 
+	int l = concat.length(); 
+
+	// Construct Z array 
+	int Z[l]; 
+	getZarr(concat, Z); 
+
+	// now looping through Z array for matching condition 
+	for (int i = 0; i < l; ++i) 
+	{ 
+		// if Z[i] (matched region) is equal to pattern 
+		// length we got the pattern 
+		if (Z[i] == pattern.length()) 
+			cout << "Pattern found at index "
+				<< i - pattern.length() -1 << endl; 
+	} 
+} 
+
+// Fills Z array for given string str[] 
+void getZarr(string str, int Z[]) 
+{ 
+	int n = str.length(); 
+	int L, R, k; 
+
+	// [L,R] make a window which matches with prefix of s 
+	L = R = 0; 
+	for (int i = 1; i < n; ++i) 
+	{ 
+		// if i>R nothing matches so we will calculate. 
+		// Z[i] using naive way. 
+		if (i > R) 
+		{ 
+			L = R = i; 
+
+			// R-L = 0 in starting, so it will start 
+			// checking from 0'th index. For example, 
+			// for "ababab" and i = 1, the value of R 
+			// remains 0 and Z[i] becomes 0. For string 
+			// "aaaaaa" and i = 1, Z[i] and R become 5 
+			while (R<n && str[R-L] == str[R]) 
+				R++; 
+			Z[i] = R-L; 
+			R--; 
+		} 
+		else
+		{ 
+			// k = i-L so k corresponds to number which 
+			// matches in [L,R] interval. 
+			k = i-L; 
+
+			// if Z[k] is less than remaining interval 
+			// then Z[i] will be equal to Z[k]. 
+			// For example, str = "ababab", i = 3, R = 5 
+			// and L = 2 
+			if (Z[k] < R-i+1) 
+				Z[i] = Z[k]; 
+
+			// For example str = "aaaaaa" and i = 2, R is 5, 
+			// L is 0 
+			else
+			{ 
+				// else start from R and check manually 
+				L = i; 
+				while (R<n && str[R-L] == str[R]) 
+					R++; 
+				Z[i] = R-L; 
+				R--; 
+			} 
+		} 
+	} 
+} 
+
+// Driver program 
+int main() 
+{ 
+	string text = "GEEKS FOR GEEKS"; 
+	string pattern = "GEEK"; 
+	search(text, pattern); 
+	return 0; 
+}