update

easy/206.reverse-linked-list.go

@@ -6,8 +6,7 @@
  * }
  */
 func reverseList(head *ListNode) *ListNode {
-	reverseRecurse(&head)
-	return head
+	return reverseRecurse(head)
 // return reverseIter(head, nil)
 }
 
@@ -21,17 +20,12 @@ func reverseIter(head, tail *ListNode) *ListNode {
 	return reverseIter(head, curr)
 }
 
-func reverseRecurse(head **ListNode) {
-	first := *head
-	if first == nil {
-		return
+func reverseRecurse(head *ListNode) *ListNode {
+	if head == nil || head.Next == nil {
+		return head
 	}
-	rest := first.Next
-	if rest == nil {
-		return
-	}
-	reverseRecurse(&rest)
-	first.Next.Next = first
-	first.Next = nil
-	*head = rest
+	newHead := reverseRecurse(head.Next)
+	head.Next.Next = head
+	head.Next = nil
+	return newHead
 }

hard/146.lru-cache.go

@@ -0,0 +1,86 @@
+type biNode struct {
+	key  int
+	val  int
+	prev *biNode
+	next *biNode
+}
+
+type LRUCache struct {
+	capacity int
+	size     int
+	cache    map[int]*biNode
+	head     *biNode
+	tail     *biNode
+}
+
+func Constructor(capacity int) LRUCache {
+	var lru LRUCache
+	lru.capacity = capacity
+	lru.cache = make(map[int]*biNode)
+	return lru
+}
+
+func (this *LRUCache) Get(key int) int {
+	if node, ok := this.cache[key]; ok {
+		this.moveToHead(node)
+		return node.val
+	}
+	return -1
+}
+
+func (this *LRUCache) Put(key int, value int) {
+	if node, ok := this.cache[key]; ok {
+		node.val = value
+		this.moveToHead(node)
+		return
+	} // Already exsist, update value & move to head
+	newHead := &biNode{key, value, nil, this.head}
+	if this.size == 0 {
+		this.head = newHead
+		this.tail = newHead
+	} else {
+		this.head.prev = newHead
+		this.head = newHead
+	}
+	this.cache[key] = this.head
+	this.size++                    // Not exsist, add new head
+	if this.size > this.capacity { // Remove tail
+		this.size--
+		delete(this.cache, this.tail.key)
+		this.tail = this.tail.prev
+		if this.tail == nil {
+			this.head = nil
+		} else {
+			this.tail.next = nil
+		}
+	}
+}
+
+func (this *LRUCache) moveToHead(node *biNode) {
+	if node == this.head {
+		return
+	}
+	if node == this.tail {
+		this.tail.next = this.head
+		this.head.prev = this.tail
+		this.head = this.tail
+		this.tail = this.tail.prev
+		this.tail.next = nil
+		this.head.prev = nil
+		return
+	}
+	prev, next := node.prev, node.next
+	next.prev = prev
+	prev.next = next
+	node.prev = nil
+	node.next = this.head
+	this.head.prev = node
+	this.head = node
+}
+
+/**
+ * Your LRUCache object will be instantiated and called as such:
+ * obj := Constructor(capacity);
+ * param_1 := obj.Get(key);
+ * obj.Put(key,value);
+ */