From 17fedf211d8833fd2514390d0d169406e4da4f9c Mon Sep 17 00:00:00 2001
From: Ju Hwijung <contact@juhwijung.com>
Date: Sun, 3 May 2026 23:39:10 +0900
Subject: [PATCH] =?UTF-8?q?9=EC=A3=BC=EC=B0=A8=20=EB=AC=B8=EC=A0=9C=20?=
 =?UTF-8?q?=ED=92=80=EC=9D=B4=205=EA=B0=9C=20=EC=B6=94=EA=B0=80?=
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---
 linked-list-cycle/hwi-middle.cpp           | 32 +++++++++
 maximum-product-subarray/hwi-middle.cpp    | 24 +++++++
 minimum-window-substring/hwi-middle.cpp    | 77 ++++++++++++++++++++
 pacific-atlantic-water-flow/hwi-middle.cpp | 81 ++++++++++++++++++++++
 sum-of-two-integers/hwi-middle.cpp         | 30 ++++++++
 5 files changed, 244 insertions(+)
 create mode 100644 linked-list-cycle/hwi-middle.cpp
 create mode 100644 maximum-product-subarray/hwi-middle.cpp
 create mode 100644 minimum-window-substring/hwi-middle.cpp
 create mode 100644 pacific-atlantic-water-flow/hwi-middle.cpp
 create mode 100644 sum-of-two-integers/hwi-middle.cpp

diff --git a/linked-list-cycle/hwi-middle.cpp b/linked-list-cycle/hwi-middle.cpp
new file mode 100644
index 0000000000..2d21e79fb8
--- /dev/null
+++ b/linked-list-cycle/hwi-middle.cpp
@@ -0,0 +1,32 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    bool hasCycle(ListNode *head) {
+        if (head == nullptr)
+        {
+            return false;
+        }
+        
+        unordered_set<ListNode*> ns;
+        ListNode* cur = head;
+        while (cur->next != nullptr)
+        {
+            if (ns.contains(cur))
+            {
+                return true;
+            }
+
+            ns.insert(cur);
+            cur = cur->next;
+        }
+
+        return false;
+    }
+};
diff --git a/maximum-product-subarray/hwi-middle.cpp b/maximum-product-subarray/hwi-middle.cpp
new file mode 100644
index 0000000000..4855084909
--- /dev/null
+++ b/maximum-product-subarray/hwi-middle.cpp
@@ -0,0 +1,24 @@
+class Solution {
+public:
+    int maxProduct(vector<int>& nums) {
+        if (nums.size() == 0) 
+        {
+            return 0;
+        }
+
+        int max_so_far = nums[0];
+        int min_so_far = nums[0];
+        int result = max_so_far;
+
+        for (int i = 1; i < nums.size(); i++) 
+        {
+            int curr = nums[i];
+            int temp_max = max(curr, max(max_so_far * curr, min_so_far * curr));
+            min_so_far = min(curr, min(max_so_far * curr, min_so_far * curr));
+            max_so_far = temp_max;
+            result = max(max_so_far, result);
+        }
+
+        return result;
+    }
+};
diff --git a/minimum-window-substring/hwi-middle.cpp b/minimum-window-substring/hwi-middle.cpp
new file mode 100644
index 0000000000..a1c37e7ac9
--- /dev/null
+++ b/minimum-window-substring/hwi-middle.cpp
@@ -0,0 +1,77 @@
+class Solution {
+public:
+    string minWindow(string s, string t) {
+        if (s.empty() || t.empty())
+        {
+            return "";
+        }
+
+        // t에서 각 문자가 등장한 횟수
+        unordered_map<char, int> dictT;
+        for (auto& c : t)
+        {
+            dictT[c]++;
+        }
+
+        // t에 들어있는 문자의 종류
+        // 즉, 윈도우 안에 있는 문자의 종류는 required개 이상이어야 함
+        int required = dictT.size();
+
+        int l = 0;
+        int r = 0;
+
+        // t에 있는 문자의 종류 중 현재 윈도우 내에서 필요한 만큼 채워진 문자의 수
+        int formed = 0;
+
+        // 윈도우에 각 문자가 등장한 횟수
+        unordered_map<char, int> windowCounts;
+
+        // 윈도우 길이, 왼쪽 인덱스, 오른쪽 인덱스
+        int ans[3] = { -1, 0, 0 };
+
+        while (r < s.length())
+        {
+            // 오른쪽 포인터가 가리키는 문자를 윈도우에 추가
+            char c = s[r];
+            windowCounts[c]++;
+
+            // t에서 등장한 횟수가 같다면 formed 증가
+            if (dictT.contains(c) && windowCounts[c] == dictT[c])
+            {
+                formed++;
+            }
+
+            // 윈도우가 조건을 만족하는 동안 루프
+            // 즉, 더 이상 조건을 만족하지 않을 때 까지 왼쪽 포인터를 이동하여 윈도우를 축소시켜봄
+            while (l <= r && formed == required)
+            {
+                c = s[l];
+                
+                // 현재까지 발견한 가장 작은 윈도우 정보를 저장
+                if (ans[0] == -1 || r - l + 1 < ans[0])
+                {
+                    ans[0] = r - l + 1;
+                    ans[1] = l;
+                    ans[2] = r;
+                }
+
+                // 왼쪽 포인터가 가리키는 문자를 윈도우에서 제거
+                windowCounts[c]--;
+
+                // 그 결과, 문자가 t에서 등장한 횟수를 충족하지 못하면 formed 감소
+                if (dictT.contains(c) && windowCounts[c] < dictT[c])
+                {
+                    formed--;
+                }
+
+                // 왼쪽 포인터 이동
+                l++;
+            }
+
+            // 축소해가며 탐색이 끝났으면 오른쪽 포인터를 이동
+            r++;
+        }
+
+        return ans[0] == -1 ? "" : s.substr(ans[1], ans[2] - ans[1] + 1);
+    }
+};
diff --git a/pacific-atlantic-water-flow/hwi-middle.cpp b/pacific-atlantic-water-flow/hwi-middle.cpp
new file mode 100644
index 0000000000..67c35f5360
--- /dev/null
+++ b/pacific-atlantic-water-flow/hwi-middle.cpp
@@ -0,0 +1,81 @@
+class Solution {
+public:
+    vector<vector<int>> pacificAtlantic(vector<vector<int>>& heights) {
+        int r = heights.size();
+        int c = heights[0].size();
+        
+        vector<vector<int>> result;
+        if (r == 0 || c == 0) return result;
+
+        vector<vector<bool>> pacific(r, vector<bool>(c, false));
+        vector<vector<bool>> atlantic(r, vector<bool>(c, false));
+        
+        queue<pair<int, int>> pacific_q;
+        queue<pair<int, int>> atlantic_q;
+
+        for (int i = 0; i < r; ++i) 
+        {
+            pacific_q.push({i, 0});
+            pacific[i][0] = true;
+            
+            atlantic_q.push({i, c - 1});
+            atlantic[i][c - 1] = true;
+        }
+
+        for (int j = 0; j < c; ++j) 
+        {
+            pacific_q.push({0, j});
+            pacific[0][j] = true;
+            
+            atlantic_q.push({r - 1, j});
+            atlantic[r - 1][j] = true;
+        }
+
+        bfs(pacific_q, pacific, heights);
+        bfs(atlantic_q, atlantic, heights);
+
+        for (int i = 0; i < r; ++i) 
+        {
+            for (int j = 0; j < c; ++j) 
+            {
+                if (pacific[i][j] && atlantic[i][j]) 
+                {
+                    result.push_back({i, j});
+                }
+            }
+        }
+
+        return result;
+    }
+
+private:
+    void bfs(queue<pair<int, int>>& q, vector<vector<bool>>& visited, const vector<vector<int>>& heights) 
+    {
+        int r = heights.size();
+        int c = heights[0].size();
+        
+        int dx[] = { 0, 1, 0, -1 };
+        int dy[] = { 1, 0, -1, 0 };
+
+        while (!q.empty()) {
+            int x, y;
+            tie(x, y) = q.front();
+            q.pop();
+
+            for (int dir = 0; dir < 4; ++dir) 
+            {
+                int nx = x + dx[dir];
+                int ny = y + dy[dir];
+
+                if (nx < 0 || nx >= r || ny < 0 || ny >= c) continue;
+                
+                if (visited[nx][ny]) continue;
+                
+                if (heights[nx][ny] < heights[x][y]) continue;
+
+                visited[nx][ny] = true;
+                q.push({nx, ny});
+            }
+        }
+    }
+};
diff --git a/sum-of-two-integers/hwi-middle.cpp b/sum-of-two-integers/hwi-middle.cpp
new file mode 100644
index 0000000000..72c83fa27f
--- /dev/null
+++ b/sum-of-two-integers/hwi-middle.cpp
@@ -0,0 +1,30 @@
+class Solution {
+public:
+    int getSum(int a, int b) {
+        int res = 0;
+        
+        bool carry = false;
+        for (int i = 0; i < 32; ++i)
+        {
+            int mask = 1 << i;
+            bool bitA = a & mask;
+            bool bitB = b & mask;
+            bool sum = adder(bitA, bitB, carry);
+            if (sum)
+            {
+                res |= mask;
+            }
+        }
+
+        return res;
+    }
+
+    bool adder(bool a, bool b, bool& inout_carry)
+    {
+        bool axorb = a ^ b;
+        bool sum = axorb ^ inout_carry;
+        bool aandb = a & b;
+        inout_carry = aandb | (axorb & inout_carry);
+        return sum;
+    }
+};