From b4000cfbdbad2123014a8d9503b64058c38a3c2f Mon Sep 17 00:00:00 2001
From: Nahid Fatma <nfatmarkl@gmail.com>
Date: Mon, 28 Oct 2019 21:16:53 +0530
Subject: [PATCH] pattern searching using Z algorithm

---
 ZAlgorithm/ZAlgorithm.java | 98 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 ZAlgorithm/ZAlgorithm.java

diff --git a/ZAlgorithm/ZAlgorithm.java b/ZAlgorithm/ZAlgorithm.java
new file mode 100644
index 0000000..e3b7537
--- /dev/null
+++ b/ZAlgorithm/ZAlgorithm.java
@@ -0,0 +1,98 @@
+class ZAlgorithm {  
+  
+    //  prints all occurrences of pattern in text using 
+    // Z algo 
+    public static void search(String text, String pattern) 
+    { 
+  
+        // Create concatenated string "P$T" 
+        String concat = pattern + "$" + text; 
+  
+        int l = concat.length(); 
+  
+        int Z[] = new int[l]; 
+  
+        // Construct Z array 
+        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()){ 
+                System.out.println("Pattern found at index "
+                              + (i - pattern.length() - 1)); 
+            } 
+        } 
+    } 
+  
+    // Fills Z array for given string str[] 
+    private static void getZarr(String str, int[] Z) { 
+  
+        int n = str.length(); 
+          
+        // [L,R] make a window which matches with  
+        // prefix of s 
+        int L = 0, 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.charAt(R - L) == str.charAt(R)) 
+                    R++; 
+                  
+                Z[i] = R - L; 
+                R--; 
+  
+            } 
+            else{ 
+  
+                // k = i-L so k corresponds to number which 
+                // matches in [L,R] interval. 
+                int 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]; 
+  
+                
+                else{ 
+  
+  
+                // else start from R and check manually 
+                    L = i; 
+                    while(R < n && str.charAt(R - L) == str.charAt(R)) 
+                        R++; 
+                      
+                    Z[i] = R - L; 
+                    R--; 
+                } 
+            } 
+        } 
+    } 
+      
+    // Driver program 
+    public static void main(String[] args)  
+    { 
+        String text = "HEY OCTOBER BRINGS HACTOBERFEST"; 
+        String pattern = "OBER"; 
+  
+        search(text, pattern); 
+    } 
+}