Data commit

Task/Entropy-Narcissist/Java/entropy-narcissist.java

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+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+public class EntropyNarcissist {
+
+    private static final String FILE_NAME = "src/EntropyNarcissist.java";
+
+    public static void main(String[] args) {
+        System.out.printf("Entropy of file \"%s\" = %.12f.%n", FILE_NAME, getEntropy(FILE_NAME));
+    }
+
+    private static double getEntropy(String fileName) {
+        Map<Character,Integer> characterCount = new HashMap<>();
+        int length = 0;
+
+        try (BufferedReader reader = new BufferedReader(new FileReader(new File(fileName)));) {
+            int c = 0;
+            while ( (c = reader.read()) != -1 ) {
+                characterCount.merge((char) c, 1, (v1, v2) -> v1 + v2);
+                length++;
+            }
+        }
+        catch ( IOException e ) {
+            throw new RuntimeException(e);
+        }
+
+        double entropy = 0;
+        for ( char key : characterCount.keySet() ) {
+            double fraction = (double) characterCount.get(key) / length;
+            entropy -= fraction * Math.log(fraction);
+        }
+
+        return entropy / Math.log(2);
+    }
+
+}