Create 0460-lfu-cache.java

Author: dmgodoy

java/0460-lfu-cache.java

@@ -0,0 +1,71 @@
+class LFUCache {
+    private static class Entry {
+        int key;
+        int value;
+        int freq;
+
+        public Entry(int key, int value, int freq) {
+            this.key = key;
+            this.value = value;
+            this.freq = freq;
+        }
+    }
+
+    private final int capacity;
+    private int minFreq = 0;
+    private final Map<Integer, Entry> entries = new HashMap<>();
+    private final Map<Integer, LinkedHashSet<Entry>> freqMap = new HashMap<>();
+
+    public LFUCache(int capacity) {
+        this.capacity = capacity;
+    }
+
+    public int get(int key) {
+        Entry e = entries.get(key);
+        if (e == null) return -1;
+        updateFrequency(e);
+        return e.value;
+    }
+
+    public void put(int key, int value) {
+        if (capacity == 0) return;
+        if (entries.containsKey(key)) {
+            Entry e = entries.get(key);
+            e.value = value;
+            updateFrequency(e);
+        } else {
+            if (entries.size() == capacity) {
+                evictLeastFrequent();
+            }
+            Entry e = new Entry(key, value, 1);
+            entries.put(key, e);
+            freqMap.computeIfAbsent(1, k -> new LinkedHashSet<>()).add(e);
+            minFreq = 1; // Reset min frequency to 1 for new entry
+        }
+    }
+
+    private void updateFrequency(Entry e) {
+        int oldFreq = e.freq;
+        int newFreq = oldFreq + 1;
+
+        freqMap.get(oldFreq).remove(e);
+        if (freqMap.get(oldFreq).isEmpty()) {
+            freqMap.remove(oldFreq);
+            if (minFreq == oldFreq) minFreq++;
+        }
+
+        e.freq = newFreq;
+        freqMap.computeIfAbsent(newFreq, k -> new LinkedHashSet<>()).add(e);
+    }
+
+    private void evictLeastFrequent() {
+        LinkedHashSet<Entry> minFreqEntries = freqMap.get(minFreq);
+        Entry toRemove = minFreqEntries.iterator().next();
+        minFreqEntries.remove(toRemove);
+        if (minFreqEntries.isEmpty()) {
+            freqMap.remove(minFreq);
+        }
+
+        entries.remove(toRemove.key);
+    }
+}