Semi #146

Author: aylei

a

@@ -140,3 +140,4 @@ mod n0140_word_break_ii;
 mod n0143_reorder_list;
 mod n0144_binary_tree_preorder_traversal;
 mod n0145_binary_tree_postorder_traversal;
+mod n0146_lru_cache;

src/lib.rs

@@ -0,0 +1,83 @@
+/**
+ * [146] LRU Cache
+ *
+ * 
+ * Design and implement a data structure for <a href="https://en.wikipedia.org/wiki/Cache_replacement_policies#LRU" target="_blank">Least Recently Used (LRU) cache</a>. It should support the following operations: get and put.
+ * 
+ * 
+ * 
+ * get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.<br>
+ * put(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.
+ * 
+ * 
+ * Follow up:<br />
+ * Could you do both operations in O(1) time complexity?
+ * 
+ * Example:
+ * 
+ * LRUCache cache = new LRUCache( 2 /* capacity */ );
+ * 
+ * cache.put(1, 1);
+ * cache.put(2, 2);
+ * cache.get(1);       // returns 1
+ * cache.put(3, 3);    // evicts key 2
+ * cache.get(2);       // returns -1 (not found)
+ * cache.put(4, 4);    // evicts key 1
+ * cache.get(1);       // returns -1 (not found)
+ * cache.get(3);       // returns 3
+ * cache.get(4);       // returns 4
+ * 
+ * 
+ */
+
+// submission codes start here
+
+/*
+ Least Recently Used, 最近最少使用, 关键在于追踪每一个 entry 的 age, 每次淘汰最小的那一个 key
+
+ 假如淘汰逻辑要做到 O(1) 复杂度, 我们可以引入一个链表, 每次 touch 一个值时, 就删掉它重新 push_back, 而当达到容量要驱逐时, 则 pop_front
+
+ Rust 的链表不支持根据引用删除任意元素，这个工程实现还是有点挑战的, 晚点再做
+ */
+use std::collections::HashMap;
+use std::collections::LinkedList;
+struct LRUCache {
+    cache: HashMap<i32, i32>,
+    vec: Vec<i32>,
+    cap: i32,
+}
+
+/** 
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl LRUCache {
+
+    fn new(capacity: i32) -> Self {
+        LRUCache{
+            cache: HashMap::with_capacity(capacity as usize,),
+            vec: Vec::with_capacity(capacity as usize),
+            cap: capacity,
+        }
+    }
+    
+    fn get(&mut self, key: i32) -> i32 {
+        let cache = HashMap::new();
+        let list = Vec::new();
+    }
+    
+    fn put(&mut self, key: i32, value: i32) {
+        
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_146() {
+    }
+}