KMP

Author: ragavi-632007

src/main/java/com/thealgorithms/KMP.java

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+public class KMP {
+
+    // Function to compute LPS array
+    public static int[] computeLPSArray(String pattern) {
+        int M = pattern.length();
+        int[] lps = new int[M];
+        int len = 0; // length of the previous longest prefix suffix
+        int i = 1;
+        lps[0] = 0; // lps[0] is always 0
+
+        while (i < M) {
+            if (pattern.charAt(i) == pattern.charAt(len)) {
+                len++;
+                lps[i] = len;
+                i++;
+            } else {
+                if (len != 0) {
+                    len = lps[len - 1];
+                } else {
+                    lps[i] = 0;
+                    i++;
+                }
+            }
+        }
+        return lps;
+    }
+
+    // KMP Search function
+    public static void KMPSearch(String pattern, String text) {
+        int M = pattern.length();
+        int N = text.length();
+
+        int[] lps = computeLPSArray(pattern);
+        int i = 0; // index for text
+        int j = 0; // index for pattern
+
+        while (i < N) {
+            if (pattern.charAt(j) == text.charAt(i)) {
+                i++;
+                j++;
+            }
+
+            if (j == M) {
+                System.out.println("Pattern found at index " + (i - j));
+                j = lps[j - 1];
+            } else if (i < N && pattern.charAt(j) != text.charAt(i)) {
+                if (j != 0)
+                    j = lps[j - 1];
+                else
+                    i++;
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        String text = "ABABDABACDABABCABAB";
+        String pattern = "ABABCABAB";
+        KMPSearch(pattern, text);
+    }
+}