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bloom_filters/src/bloom_filters/Main.java

@@ -36,9 +36,66 @@ class Hash {
     }
 }
 
-class Examples {
-    void testTheThing(Tester t) {
-        t.checkExpect(true, true);
-        t.checkExpect(false, false);
+class Bloom {
+    int n;       // Number of things added.
+    int m;       // The length of the buffer.
+    int k;       // The number of hash functions to apply.
+    boolean[] v; // The bit vector.
+
+    Bloom(int k, int m) {
+        if (k < 1 || m < 1)
+            throw new IllegalArgumentException("Need bigger arguments.");
+
+        this.m = m;
+        this.k = k;
+        this.v = new boolean[m]; // Initialize the bit vector.
+    }
+
+    void add(Object o) { // Apply the hash functions.
+        // Get the array of hashes for an object.
+        int[] hashes = Hash.hash(o, this.k, this.m);
+        // Set those elements in the vector to true.
+        for (int h : hashes) this.v[h] = true;
+        this.n++;
+    }
+
+    // Returns true if it might contain the object, false if it definitely does
+    // not.
+    boolean has(Object o) {
+        // Get the array of hashes for an object.
+        int[] hashes = Hash.hash(o, this.k, this.m);
+        // Check that all of those are true.
+        for (int h : hashes)
+            if (!this.v[h]) return false;
+        return true;
+    }
+
+    // Predict the false positive rate.
+    double probT2() {
+        return Math.pow(
+            1 - Math.pow(Math.E, ((-this.k * this.n) / this.m)), this.k
+        );
+    }
+
+    // Return the number of elements added.
+    int added() { return this.n; }
+
+    void clear() {
+        this.v = new boolean[this.m];
+        this.n = 0;
+    }
+}
+
+class Examples {
+    void testBloomAddAndHas(Tester t) {
+        Bloom b = new Bloom(2, 8);
+        t.checkExpect(b.has(7), false);
+        b.add(1);
+        t.checkExpect(b.has(1), true);
+        b.add(2);
+        b.add(3);
+        t.checkExpect(b.has(2) && b.has(3), true);
+        t.checkExpect(b.has(0), false);
+        t.checkExpect(b.added(), 3);
     }
 }