力扣labuladong——一刷day89

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前言

LFU 算法是要复杂很多的，而且经常出现在面试中，因为 LFU 缓存淘汰算法在工程实践中经常使用，也有可能是因为 LRU 算法太简单了。不过话说回来，这种著名的算法的套路都是固定的，关键是由于逻辑较复杂，不容易写出漂亮且没有 bug 的代码

一、力扣460. LFU 缓存

class LFUCache {
   
    private int cap;
    private int minFreq;
    private HashMap<Integer,Integer> keyToVal;
    private HashMap<Integer,Integer> keyToFreq;
    private HashMap<Integer,LinkedHashSet<Integer>> freqToKeys;

    public LFUCache(int capacity) {
   
        this.cap = capacity;
        minFreq = 0;
        keyToVal = new HashMap<>();
        keyToFreq = new HashMap<>();
        freqToKeys = new HashMap<>();
    }
    
    public int get(int key) {
   
        if(!keyToVal.containsKey(key)){
   
            return -1;
        }
        increase(key);
        return keyToVal.get(key);
    }
    
    public void put(int key, int value) {
   
        if(cap <= 0)return;
        if(keyToVal.containsKey(key)){
   
            keyToVal.put(key,value);
            increase(key);
            return;
        }
        if(cap <= keyToVal.size()){
   
            removeMinFreq();
        }
        keyToVal.put(key,value);
        keyToFreq.put(key,1);
        freqToKeys.putIfAbsent(1,new LinkedHashSet<Integer>());
        freqToKeys.get(1).add(key);
        this.minFreq = 1;
    }
    private void increase(int key){
   
        int freq = keyToFreq.get(key);
        keyToFreq.put(key,freq+1);
        freqToKeys.get(freq).remove(key);
        freqToKeys.putIfAbsent(freq+1,new LinkedHashSet<Integer>());
        freqToKeys.get(freq+1).add(key);
        if(freqToKeys.get(freq).isEmpty()){
   
            freqToKeys.remove(freq);
            if(freq == minFreq){
   
                this.minFreq ++;
            }
        }
    }
    private void removeMinFreq(){
   
        LinkedHashSet<Integer> list = freqToKeys.get(this.minFreq);
        int key = list.iterator().next();
        list.remove(key);
        if(list.isEmpty()){
   
            freqToKeys.remove(this.minFreq);
        }
        keyToFreq.remove(key);
        keyToVal.remove(key);
    }
}

/**
 * Your LFUCache object will be instantiated and called as such:
 * LFUCache obj = new LFUCache(capacity);
 * int param_1 = obj.get(key);
 * obj.put(key,value);
 */