Adding KMP String Matching Algorithm

src/chapter15stringalgorithms/KMPStringMatchingAlgorithm.java

@@ -0,0 +1,80 @@
+package chapter15stringalgorithms;
+
+import java.io.*;
+
+public class KMPStringMatchingAlgorithm {
+
+    public static void main(String[] args) throws Exception {
+        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+        int tc = Integer.parseInt(br.readLine());
+        while(tc-->0) {
+            String[] input = br.readLine().split(" ");
+            char[] pattern = input[0].toCharArray();
+            char[] text = input[1].toCharArray();
+            if(pattern.length==1){
+                bw.write(String.valueOf(getNoOfMatchedString(text,pattern)));
+            } else {
+                bw.write(String.valueOf(getNoOfMatchedStrings(text,pattern)));
+            }
+
+            bw.newLine();
+        }
+        bw.close();
+    }
+
+    private static int getNoOfMatchedString(char[] text, char[] pattern) {
+        char p = pattern[0];
+        int count = 0;
+        for(int idx=0;idx<text.length;idx++){
+            if(text[idx]==p){
+                count++;
+            }
+        }
+        return count;
+    }
+
+    public static int getNoOfMatchedStrings(char[] text, char[] pattern){
+        int p1=0;
+        int p2=0;
+        int count = 0;
+        int[] lps = getLPS(pattern);
+        while(p1<text.length){
+            if(text[p1]==pattern[p2]){
+                if(p2==pattern.length-1){
+                    count++;
+                    p2=lps[p2-1];
+                } else {
+                    p1++;
+                    p2++;
+                }
+            } else if(p2>0){
+                p2 = lps[p2-1];
+            } else {
+                p1++;
+            }
+        }
+        return count;
+    }
+
+    public static int[] getLPS(char[] pattern){
+        int[] lps = new int[pattern.length];
+        int p1 = 0;
+        int p2 = 1;
+        lps[0] = 0;
+        while(p2<pattern.length){
+            if(pattern[p2]==pattern[p1]){
+                lps[p2]=p1+1;
+                p1++;
+                p2++;
+            } else if(p1>0){
+                p1 = lps[p1-1];
+            } else {
+                lps[p2]=0;
+                p2++;
+            }
+        }
+        return lps;
+    }
+}