feat: Make the OpBuilder work only for PositiveBlob

src/rank/distinct_map.rs

@@ -0,0 +1,65 @@
+use std::collections::HashMap;
+use std::hash::Hash;
+
+pub struct DistinctMap<K> {
+    inner: HashMap<K, usize>,
+    limit: usize,
+    len: usize,
+}
+
+impl<K: Hash + Eq> DistinctMap<K> {
+    pub fn new(limit: usize) -> Self {
+        DistinctMap {
+            inner: HashMap::new(),
+            limit: limit,
+            len: 0,
+        }
+    }
+
+    pub fn digest(&mut self, key: K) -> bool {
+        let seen = self.inner.entry(key).or_insert(0);
+        if *seen < self.limit {
+            *seen += 1;
+            self.len += 1;
+            true
+        } else {
+            false
+        }
+    }
+
+    pub fn accept_without_key(&mut self) -> bool {
+        self.len += 1;
+        true
+    }
+
+    pub fn len(&self) -> usize {
+        self.len
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn easy_distinct_map() {
+        let mut map = DistinctMap::new(2);
+        for x in &[1, 1, 1, 2, 3, 4, 5, 6, 6, 6, 6, 6] {
+            map.digest(x);
+        }
+        assert_eq!(map.len(), 8);
+
+        let mut map = DistinctMap::new(2);
+        assert_eq!(map.digest(1), true);
+        assert_eq!(map.digest(1), true);
+        assert_eq!(map.digest(1), false);
+        assert_eq!(map.digest(1), false);
+
+        assert_eq!(map.digest(2), true);
+        assert_eq!(map.digest(3), true);
+        assert_eq!(map.digest(2), true);
+        assert_eq!(map.digest(2), false);
+
+        assert_eq!(map.len(), 5);
+    }
+}