Create longestpreffix.java

longestpreffix.java

@@ -0,0 +1,59 @@
+package string;
+
+public class longestpreffix {
+    static int longestPrefixSuffix(String s) {
+        int n = s.length();
+
+        int lps[] = new int[n];
+
+        // lps[0] is always 0
+        lps[0] = 0;
+
+        // length of the previous
+        // longest prefix suffix
+        int len = 0;
+
+        // the loop calculates lps[i]
+        // for i = 1 to n-1
+        int i = 1;
+        while (i < n) {
+            if (s.charAt(i) == s.charAt(len)) {
+                len++;
+                lps[i] = len;
+                i++;
+            }
+
+            // (pat[i] != pat[len])
+            else {
+                // This is tricky. Consider
+                // the example. AAACAAAA
+                // and i = 7. The idea is
+                // similar to search step.
+                if (len != 0) {
+                    len = lps[len - 1];
+
+                    // Also, note that we do
+                    // not increment i here
+                }
+
+                // if (len == 0)
+                else {
+                    lps[i] = 0;
+                    i++;
+                }
+            }
+        }
+
+        int res = lps[n - 1];
+
+        // Since we are looking for
+        // non overlapping parts.
+        return (res > n / 2) ? n / 2 : res;
+    }
+
+    // Driver program
+    public static void main(String[] args) {
+        String s = "abcab";
+        System.out.println(longestPrefixSuffix(s));
+    }
+}