add inerview codes.

.drone.yml

@@ -14,3 +14,6 @@ steps:
       - cd stl || exit
       - g++ map.cpp -o map && ./map
       - cd ..
+
+      - cd interview || exit
+      - g++ memcache.cpp -o memcache && ./memcache

interview/memcache.cpp

@@ -0,0 +1,109 @@
+#include <iostream>
+#include <vector>
+#include <map>
+#define RES_MAX 5
+using namespace std;
+
+struct list
+{
+    list *next = NULL;
+    int k = 0;
+};
+
+class Mem
+{
+public:
+    int get(int k)
+    {
+        if (memcache.find(k) != memcache.end())
+        {
+            // cache hit: update visit list
+            for (list **node = &visit; *node; node = &((*node)->next))
+            {
+                if ((*node)->k == k)
+                {
+                    list *found = *node;
+                    *node = (*node)->next;
+                    found->next = visit;
+                    visit = found;
+                    break;
+                }
+            }
+            return memcache.find(k)->second;
+        }
+        else
+        {
+            // cache miss:
+            if (memcache.size() < RES_MAX)
+            {
+                // if cache available: update visit list; update memcache
+                list *node = new list;
+                node->k = k;
+                node->next = visit;
+                visit = node;
+                memcache.emplace(k, 0);
+            }
+            else
+            {
+                // if cache full: swap out oldest memcache; rm oldest visit; update visit
+                for (list **node = &visit; *node; node = &(*node)->next)
+                {
+                    if ((*node)->next == NULL)
+                    {
+                        memcache.erase(memcache.find((*node)->k));
+                        delete *node;
+                        *node = NULL;
+                        memcache.emplace(k, 0);
+                        break;
+                    }
+                }
+                list *node = new list;
+                node->k = k;
+                node->next = visit;
+                visit = node;
+            }
+            return 0;
+        }
+    }
+    int set(int k, int v)
+    {
+        if (get(k) != v)
+        {
+            memcache.find(k)->second = v;
+        }
+        return memcache.find(k)->second;
+    }
+    void print()
+    {
+        for (const auto &byte : memcache)
+        {
+            cout << byte.first << ": " << byte.second << endl;
+        }
+        for (list *node = visit; node; node = node->next)
+        {
+            cout << " -> " << node->k;
+        }
+        cout << endl;
+    }
+
+private:
+    map<int, int> memcache;
+    list *visit = NULL;
+};
+
+int main()
+{
+    Mem mem;
+    for (int i = 10; i > 0; i--)
+    {
+        mem.get(i);
+    }
+    for (int i = 4; i < 7; i++)
+    {
+        if (mem.set(i, i) != i)
+        {
+            cout << "insert " << i << " failed" << endl;
+        }
+    }
+    mem.print();
+}