diff --git a/contains-duplicate/hwi-middle.cpp b/contains-duplicate/hwi-middle.cpp
new file mode 100644
index 000000000..4f1778df3
--- /dev/null
+++ b/contains-duplicate/hwi-middle.cpp
@@ -0,0 +1,7 @@
+class Solution {
+public:
+    bool containsDuplicate(vector<int>& nums) {
+        sort(nums.begin(), nums.end());
+        return nums.end() != unique(nums.begin(), nums.end());
+    }
+};
diff --git a/house-robber/hwi-middle.cpp b/house-robber/hwi-middle.cpp
new file mode 100644
index 000000000..918933851
--- /dev/null
+++ b/house-robber/hwi-middle.cpp
@@ -0,0 +1,15 @@
+class Solution {
+public:
+    int rob(vector<int>& nums) {
+        int len = nums.size() + 1;
+        vector<int> d(len);
+        d[0] = 0;
+        d[1] = nums[0];
+        for(int i = 2; i < len; ++i)
+        {
+            d[i] = max(d[i - 1], d[i - 2] + nums[i - 1]);
+        }
+
+        return d[len - 1];
+    }
+};
diff --git a/longest-consecutive-sequence/hwi-middle.cpp b/longest-consecutive-sequence/hwi-middle.cpp
new file mode 100644
index 000000000..f8e84e5f3
--- /dev/null
+++ b/longest-consecutive-sequence/hwi-middle.cpp
@@ -0,0 +1,39 @@
+class Solution {
+public:
+    int longestConsecutive(vector<int>& nums) {
+        if (nums.empty())
+        {
+            return 0;
+        }
+        
+        unordered_set<int> s;
+        s.reserve(nums.size());
+        s.max_load_factor(0.4f);
+        s.insert(nums.begin(), nums.end());
+
+        int ans = 0;
+        for(auto& e : s)
+        {
+            if (s.contains(e - 1))
+            {
+                continue;
+            }
+
+            int con = 1;
+            int num = e;
+            while (true)
+            {
+                num++;
+                if(!s.contains(num))
+                {
+                    break;
+                }
+
+                con++;
+            }
+            ans = max(ans, con);
+        }
+
+        return ans;
+    }
+};
diff --git a/top-k-frequent-elements/hwi-middle.cpp b/top-k-frequent-elements/hwi-middle.cpp
new file mode 100644
index 000000000..c49ada2a7
--- /dev/null
+++ b/top-k-frequent-elements/hwi-middle.cpp
@@ -0,0 +1,24 @@
+class Solution {
+public:
+    vector<int> topKFrequent(vector<int>& nums, int k) {
+        unordered_map<int, int> m;
+        for(auto n : nums) 
+        {
+            ++m[n];
+        }
+
+        vector<pair<int, int>> v(m.begin(), m.end());
+        sort(v.begin(), v.end(), [](const auto& a, const auto& b)
+        {
+            return a.second > b.second;
+        });
+
+        vector<int> ans;
+        ans.reserve(k);
+        for (int i = 0; i < k; ++i)
+        {
+            ans.push_back(v[i].first);
+        }
+        return ans;
+    }
+};
diff --git a/two-sum/hwi-middle.cpp b/two-sum/hwi-middle.cpp
new file mode 100644
index 000000000..ffa8cd8b5
--- /dev/null
+++ b/two-sum/hwi-middle.cpp
@@ -0,0 +1,23 @@
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        vector<int> v(2);
+        unordered_map<int, int> m;
+        for (int i = 0; i < nums.size(); ++i)
+        {
+            int num = nums[i];
+            if (m.contains(target - num))
+            {
+                v[0] = m[target - num];
+                v[1] = i;
+                return v;
+            }
+
+            m[num] = i;
+        }
+
+        v[0] = -1;
+        v[1] = -1;
+        return v;
+    }
+};