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Commit b3065b4

Browse files
solves lru cache
1 parent fb52881 commit b3065b4

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2 files changed

+85
-1
lines changed

2 files changed

+85
-1
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β€ŽREADME.md

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| 143 | [Reorder List](https://leetcode.com/problems/reorder-list) | | |
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| 144 | [Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal) | [![Java](assets/java.png)](src/BinaryTreePreOrderTraversal.java) [![Python](assets/python.png)](python/binary_tree_preorder_traversal.py) | |
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| 145 | [Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal) | [![Java](assets/java.png)](src/BinaryTreePostorderTraversal.java) [![Python](assets/python.png)](python/binary_tree_postorder_traversal.py) | |
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| 146 | [LRU Cache](https://leetcode.com/problems/lru-cache) | | |
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| 146 | [LRU Cache](https://leetcode.com/problems/lru-cache) | [![Java](assets/java.png)](src/LRUCache.java) | |
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| 147 | [Insertion Sort List](https://leetcode.com/problems/insertion-sort-list) | | |
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| 148 | [Sort List](https://leetcode.com/problems/sort-list) | | |
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| 150 | [Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation) | | |

β€Žsrc/LRUCache.java

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// T: O(n)
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// S: O(n)
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import java.util.HashMap;
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import java.util.Map;
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public class LRUCache {
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private static class Node {
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int key;
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int value;
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Node next;
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Node previous;
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Node() { }
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Node(int key, int value) {
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this.key = key;
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this.value = value;
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}
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}
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private final int capacity;
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private final Map<Integer, Node> cache = new HashMap<>();
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private Node head, tail;
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public LRUCache(int capacity) {
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this.capacity = capacity;
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head = new Node();
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tail = new Node();
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head.next = tail;
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tail.previous = head;
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}
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public int get(int key) {
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Node node = cache.get(key);
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if(node == null) {
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return -1;
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}
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moveToHead(node);
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return node.value;
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}
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public void put(int key, int value) {
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Node node = cache.get(key);
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if(node == null) {
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Node newNode = new Node(key, value);
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this.cache.put(key, newNode);
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this.addNode(newNode);
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if(cache.size() > capacity){
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Node tail = popTail();
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this.cache.remove(tail.key);
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}
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} else {
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node.value = value;
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moveToHead(node);
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}
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}
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private Node popTail(){
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Node res = tail.previous;
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this.removeNode(res);
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return res;
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}
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private void addNode(Node node) {
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node.previous = head;
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node.next = head.next;
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head.next.previous = node;
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head.next = node;
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}
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private void removeNode(Node node){
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Node pre = node.previous;
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Node post = node.next;
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pre.next = post;
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post.previous = pre;
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}
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private void moveToHead(Node node){
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this.removeNode(node);
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this.addNode(node);
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}
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}

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