From be7b1c80582197264be3e2224cd1ed8d7dbac39f Mon Sep 17 00:00:00 2001
From: ktony <k.tony9412@gmail.com>
Date: Mon, 11 Nov 2024 00:20:48 -0500
Subject: [PATCH 1/4] Reverse Bits

---
 reverse-bits/TonyKim9401.java | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 reverse-bits/TonyKim9401.java

diff --git a/reverse-bits/TonyKim9401.java b/reverse-bits/TonyKim9401.java
new file mode 100644
index 000000000..a1d107579
--- /dev/null
+++ b/reverse-bits/TonyKim9401.java
@@ -0,0 +1,14 @@
+public class Solution {
+    public int reverseBits(int n) {
+        // time complexity O(1)
+        // space complexity O(1)
+        int output = 0;
+
+        for (int i = 0; i < Integer.SIZE; i++) {
+            output <<= 1;
+            output += n & 1;
+            n >>= 1;
+        }
+        return output;
+    }
+}

From 7f781840d18c7f8d56fedda58856e7f9082fb03b Mon Sep 17 00:00:00 2001
From: ktony <k.tony9412@gmail.com>
Date: Mon, 11 Nov 2024 12:54:52 -0500
Subject: [PATCH 2/4] Binary Tree Level Order Traversal

---
 .../TonyKim9401.java                          | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 binary-tree-level-order-traversal/TonyKim9401.java

diff --git a/binary-tree-level-order-traversal/TonyKim9401.java b/binary-tree-level-order-traversal/TonyKim9401.java
new file mode 100644
index 000000000..4ec55bd91
--- /dev/null
+++ b/binary-tree-level-order-traversal/TonyKim9401.java
@@ -0,0 +1,26 @@
+// TC: O(n)
+// need to visit all nodes
+// SC: O(n)
+// normally O(log n) required however, O(n) in the worst case
+class Solution {
+    private List<List<Integer>> output = new ArrayList<>();
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        dsf(0, root);
+        return output;
+    }
+
+    private void dsf(int level, TreeNode node) {
+        if (node == null) return;
+
+        if (output.size() == level) {
+            List<Integer> inside = new ArrayList<>();
+            inside.add(node.val);
+            output.add(inside);
+        } else {
+            output.get(level).add(node.val);
+        }
+        level += 1;
+        dsf(level, node.left);
+        dsf(level, node.right);
+    }
+}

From f6027a786377e5039d9766a08f95770c37880180 Mon Sep 17 00:00:00 2001
From: ktony <k.tony9412@gmail.com>
Date: Tue, 12 Nov 2024 12:29:06 -0500
Subject: [PATCH 3/4] House Robber II & Type

---
 .../TonyKim9401.java                          |  8 ++---
 house-robber-ii/TonyKim9401.java              | 32 +++++++++++++++++++
 2 files changed, 36 insertions(+), 4 deletions(-)
 create mode 100644 house-robber-ii/TonyKim9401.java

diff --git a/binary-tree-level-order-traversal/TonyKim9401.java b/binary-tree-level-order-traversal/TonyKim9401.java
index 4ec55bd91..127b79377 100644
--- a/binary-tree-level-order-traversal/TonyKim9401.java
+++ b/binary-tree-level-order-traversal/TonyKim9401.java
@@ -5,11 +5,11 @@
 class Solution {
     private List<List<Integer>> output = new ArrayList<>();
     public List<List<Integer>> levelOrder(TreeNode root) {
-        dsf(0, root);
+        dfs(0, root);
         return output;
     }
 
-    private void dsf(int level, TreeNode node) {
+    private void dfs(int level, TreeNode node) {
         if (node == null) return;
 
         if (output.size() == level) {
@@ -20,7 +20,7 @@ private void dsf(int level, TreeNode node) {
             output.get(level).add(node.val);
         }
         level += 1;
-        dsf(level, node.left);
-        dsf(level, node.right);
+        dfs(level, node.left);
+        dfs(level, node.right);
     }
 }
diff --git a/house-robber-ii/TonyKim9401.java b/house-robber-ii/TonyKim9401.java
new file mode 100644
index 000000000..87c047264
--- /dev/null
+++ b/house-robber-ii/TonyKim9401.java
@@ -0,0 +1,32 @@
+// TC: O(n)
+// visit all nums at least once
+// SC: O(1)
+// only constant memory space required
+class Solution {
+    public int rob(int[] nums) {
+        if (nums.length == 1) return nums[0];
+
+        int prev = 0;
+        int post = 0;
+        int output1 = 0;
+
+        for (int i = 0; i < nums.length - 1; i++) {
+            int temp = prev;
+            prev = Math.max(post + nums[i], prev);
+            post = temp;
+        }
+        output1 = prev;
+
+        prev = 0;
+        post = 0;
+        int output2 = 0;
+        for (int i = 1; i < nums.length; i++) {
+            int temp = prev;
+            prev = Math.max(post + nums[i], prev);
+            post = temp;
+        }
+        output2 = prev;
+
+        return Math.max(output1, output2);
+    }
+}

From b66b35ead7e4c199372e8f63cbcda08a9e1e9704 Mon Sep 17 00:00:00 2001
From: ktony <k.tony9412@gmail.com>
Date: Wed, 13 Nov 2024 21:51:24 -0500
Subject: [PATCH 4/4] Meeting Rooms II

---
 meeting-rooms-ii/TonyKim9401.java | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 meeting-rooms-ii/TonyKim9401.java

diff --git a/meeting-rooms-ii/TonyKim9401.java b/meeting-rooms-ii/TonyKim9401.java
new file mode 100644
index 000000000..e58e18540
--- /dev/null
+++ b/meeting-rooms-ii/TonyKim9401.java
@@ -0,0 +1,22 @@
+// TC: O(n)
+// visit all intervals to compare each of start time
+// SC: O(n)
+// PQ save all intervals in the worst case
+public class Solution {
+    public int minMeetingRooms(List<Interval> intervals) {
+        if (intervals == null || intervals.isEmpty()) return 0;
+
+        intervals.sort((a, b) -> a.start - b.start);
+
+        PriorityQueue<Integer> endTimes = new PriorityQueue<>();
+        endTimes.add(intervals.get(0).end);
+
+        for (int i = 1; i < intervals.size(); i++) {
+            Interval current = intervals.get(i);
+            if (current.start >= endTimes.peek()) endTimes.poll();
+            endTimes.add(current.end);
+        }
+
+        return endTimes.size();
+    }
+}