Merge pull request #6764 from laughing-nerd/master

Implemented LRU cache in Go

code/data_structures/src/DoubleLinkedList/lru_cache_with_dll/src_go/main.go

@@ -0,0 +1,123 @@
+/*
+- LRU cache implementation in Go
+- Change the 'capacity' variable to adjust the size of cache
+- Each node in the DLL can contain a key and a value
+- There are 2 main functions:
+    1. update(key, value): If the key-value pair is absent, then it will add it to the cache. If the key is already present, then it will update its value
+    2. get(key): It will print the key's value. If the key doesn't exist then it will print -1
+- traverse() is an additional function that can be used to visualize the DLL
+- The attach() function is used to attach a node just after 'head'
+- The detach() function is used to detach a node
+
+*/
+package main
+
+import "fmt"
+
+const capacity int = 2 // Capacity of the cache. Change it accordingly
+
+type node struct{
+  data_key  int
+  data_val  int
+  next      *node
+  prev      *node
+}
+
+var head *node
+var tail *node
+var tracker map[int]*node
+
+
+
+///////////////////////////////////////
+// Helper functions                  //
+///////////////////////////////////////
+func attach(block *node){
+  // Update the DLL
+  block.next = head.next
+  (head.next).prev = block
+  head.next = block
+  block.prev = head
+
+}
+func detach(block *node){
+  //Detach the block
+  (block.prev).next = block.next
+  (block.next).prev = block.prev
+}
+
+
+func update(key int, value int){
+  // If key is already present, then update the value
+  v, found := tracker[key]
+  if found{
+    v.data_val = value
+    detach(v)
+    attach(v)
+    return
+  }
+
+  // If key is absent
+  nodeToAdd := &node{ data_key: key, data_val:value } // The node/block to be inserted
+  if len(tracker) == capacity{
+
+    nodeToRemove := tail.prev
+    detach(nodeToRemove)
+    delete(tracker, nodeToRemove.data_key) // Update the map accordingly
+    attach(nodeToAdd)
+    tracker[key] = nodeToAdd // Add the item to the map
+
+
+  } else {
+    attach(nodeToAdd)
+    tracker[key] = nodeToAdd // Add the item to the map
+  }
+
+}
+
+func get(key int){
+  // Return the value
+  reqdNode, found := tracker[key]
+  if found{
+    fmt.Printf("For key = %d, value = %d\n",key,reqdNode.data_val)
+  } else {
+    fmt.Printf("For key = %d, value = %d\n", key, -1)
+    return
+  }
+  // Update the DLL
+  detach(reqdNode)
+  attach(reqdNode)
+
+}
+
+// Visualize the DLL
+func traverse(){
+  fmt.Println("\nHere's your DLL...")
+  temp:=head.next
+  for temp != tail{
+    fmt.Printf("(%d,%d) ", temp.data_key, temp.data_val)
+    temp=temp.next
+  }
+  fmt.Println()
+}
+
+func main(){
+
+  head = &node{ data_key: 0, data_val: 0 }
+  tail = &node{ data_key: 0, data_val: 0, prev: head }
+  head.next = tail
+  tracker = make(map[int]*node)
+
+  // Sample Operations
+  update(1, 1)
+  update(2, 2)
+  get(1)      // prints 1
+  update(3,3)
+  get(2)      // prints -1
+  update(4,4) 
+  get(1)      // prints -1
+  get(3)      // prints 3
+  get(4)      // prints 4
+
+  traverse()
+}