From d57d3349dbbc0846202c00ca6fd0fd04b71d167a Mon Sep 17 00:00:00 2001
From: forest000014 <forest000014@gmail.com>
Date: Thu, 6 Mar 2025 00:14:34 +0900
Subject: [PATCH 1/5] DaleStudy#231 Meeting Rooms
---
meeting-rooms/forest000014.java | 15 +++++++++++++++
1 file changed, 15 insertions(+)
create mode 100644 meeting-rooms/forest000014.java
diff --git a/meeting-rooms/forest000014.java b/meeting-rooms/forest000014.java
new file mode 100644
index 000000000..56477d465
--- /dev/null
+++ b/meeting-rooms/forest000014.java
@@ -0,0 +1,15 @@
+/*
+# Time Complexity: O(nlogn)
+# Space Complexity: O(1)
+*/
+class Solution {
+ public boolean canAttendMeetings(int[][] intervals) {
+ Arrays.sort(intervals, (a, b) -> a[0] - b[0]);
+
+ for (int i = 1; i < intervals.length; i++) {
+ if (intervals[i][0] < intervals[i - 1][1]) return false;
+ }
+
+ return true;
+ }
+}
From 43c4a66a430b9018532958c9026e5778bdd0428f Mon Sep 17 00:00:00 2001
From: forest000014 <forest000014@gmail.com>
Date: Thu, 6 Mar 2025 00:15:03 +0900
Subject: [PATCH 2/5] DaleStudy#249 Lowest Common Ancestor of a Binary Search
Tree
---
.../forest000014.java | 28 +++++++++++++++++++
1 file changed, 28 insertions(+)
create mode 100644 lowest-common-ancestor-of-a-binary-search-tree/forest000014.java
diff --git a/lowest-common-ancestor-of-a-binary-search-tree/forest000014.java b/lowest-common-ancestor-of-a-binary-search-tree/forest000014.java
new file mode 100644
index 000000000..b40d1544f
--- /dev/null
+++ b/lowest-common-ancestor-of-a-binary-search-tree/forest000014.java
@@ -0,0 +1,28 @@
+/*
+# Time Complexity: O(n)
+# Space Compleixty: O(1)
+*/
+
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode(int x) { val = x; }
+ * }
+ */
+
+class Solution {
+ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+ // null check unnecessary
+
+ if (root.val > p.val && root.val > q.val) {
+ return lowestCommonAncestor(root.left, p, q);
+ } else if (root.val < p.val && root.val < q.val) {
+ return lowestCommonAncestor(root.right, p, q);
+ } else {
+ return root;
+ }
+ }
+}
From 12171bc25ac4ec31ae27091015162cc73225a361 Mon Sep 17 00:00:00 2001
From: forest000014 <forest000014@gmail.com>
Date: Thu, 6 Mar 2025 00:15:51 +0900
Subject: [PATCH 3/5] DaleStudy#252 Kth Smallest Element In a Bst
---
.../forest000014.java | 53 +++++++++++++++++++
1 file changed, 53 insertions(+)
create mode 100644 kth-smallest-element-in-a-bst/forest000014.java
diff --git a/kth-smallest-element-in-a-bst/forest000014.java b/kth-smallest-element-in-a-bst/forest000014.java
new file mode 100644
index 000000000..c0ee7aea9
--- /dev/null
+++ b/kth-smallest-element-in-a-bst/forest000014.java
@@ -0,0 +1,53 @@
+/*
+# Time Complexity: O(n)
+# Space Complexity: O(n)
+
+heap을 사용한 풀이, in-order traversal을 사용한 풀이 풀어볼 것!
+*/
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode() {}
+ * TreeNode(int val) { this.val = val; }
+ * TreeNode(int val, TreeNode left, TreeNode right) {
+ * this.val = val;
+ * this.left = left;
+ * this.right = right;
+ * }
+ * }
+ */
+class Solution {
+ public int kthSmallest(TreeNode root, int k) {
+ Map<TreeNode, Integer> sizes = new HashMap<>();
+
+ calculateSize(root, sizes);
+
+ return findKth(root, k, sizes);
+ }
+
+ private int calculateSize(TreeNode root, Map<TreeNode, Integer> sizes) {
+ if (root == null) return 0;
+
+ int left = calculateSize(root.left, sizes);
+ int right = calculateSize(root.right, sizes);
+
+ sizes.put(root, left + right + 1);
+ return left + right + 1;
+ }
+
+ private int findKth(TreeNode root, int k, Map<TreeNode, Integer> sizes) {
+ int left = (root.left == null) ? 0 : sizes.get(root.left);
+ int right = (root.right == null) ? 0 : sizes.get(root.right);
+
+ if (left == k - 1) {
+ return root.val;
+ } else if (left >= k) {
+ return findKth(root.left, k, sizes);
+ } else {
+ return findKth(root.right, k - left - 1, sizes);
+ }
+ }
+}
From 76d9a267f1d408e01a595f5f563179332c9e1e09 Mon Sep 17 00:00:00 2001
From: forest000014 <forest000014@gmail.com>
Date: Thu, 6 Mar 2025 00:17:23 +0900
Subject: [PATCH 4/5] DaleStudy#289 Find Median from Data Stream
---
.../forest000014.java | 49 +++++++++++++++++++
1 file changed, 49 insertions(+)
create mode 100644 find-median-from-data-stream/forest000014.java
diff --git a/find-median-from-data-stream/forest000014.java b/find-median-from-data-stream/forest000014.java
new file mode 100644
index 000000000..e7f3f76c9
--- /dev/null
+++ b/find-median-from-data-stream/forest000014.java
@@ -0,0 +1,49 @@
+/*
+# Time Complexity: O(nlogn)
+# Space Complexity: O(nlogn)
+
+*/
+class MedianFinder {
+
+ private PriorityQueue<Integer> pq1; // 1번째 ~ 가운데 원소 (max heap)
+ private PriorityQueue<Integer> pq2; // 가운데+1번째 ~ 마지막 원소 (min heap)
+
+ public MedianFinder() {
+ pq1 = new PriorityQueue<>(Collections.reverseOrder());
+ pq2 = new PriorityQueue<>();
+ }
+
+ public void addNum(int num) {
+
+ if (pq1.size() == pq2.size()) {
+ if (pq1.peek() == null || pq1.peek() >= num) {
+ pq1.add(num);
+ } else {
+ pq2.add(num);
+ pq1.add(pq2.poll());
+ }
+ } else {
+ if (pq1.peek() == null || pq1.peek() >= num) {
+ pq1.add(num);
+ pq2.add(pq1.poll());
+ } else {
+ pq2.add(num);
+ }
+ }
+ }
+
+ public double findMedian() {
+ if (pq1.size() == pq2.size()) {
+ return (pq1.peek() + pq2.peek()) / 2.0;
+ } else {
+ return pq1.peek();
+ }
+ }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * MedianFinder obj = new MedianFinder();
+ * obj.addNum(num);
+ * double param_2 = obj.findMedian();
+ */
From 2dc08273fe40c944fc00e631a6471e2adc5acf45 Mon Sep 17 00:00:00 2001
From: forest000014 <forest000014@gmail.com>
Date: Thu, 6 Mar 2025 23:43:53 +0900
Subject: [PATCH 5/5] DaleStudy#277 Insert Interval
---
insert-interval/forest000014.java | 34 +++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
create mode 100644 insert-interval/forest000014.java
diff --git a/insert-interval/forest000014.java b/insert-interval/forest000014.java
new file mode 100644
index 000000000..0488e75d3
--- /dev/null
+++ b/insert-interval/forest000014.java
@@ -0,0 +1,34 @@
+/*
+# Time Complexity: O(n)
+# Space Complexity: O(1)
+*/
+class Solution {
+ public int[][] insert(int[][] intervals, int[] newInterval) {
+ ArrayList<int[]> answer = new ArrayList<>();
+
+ int i = 0;
+ int n = intervals.length;
+
+ // newInterval보다 왼쪽의 구간들 추가
+ while (i < n && intervals[i][1] < newInterval[0]) {
+ answer.add(intervals[i]);
+ i++;
+ }
+
+ // newInterval과 겹치는 구간들 병합
+ while (i < n && intervals[i][0] <= newInterval[1]) {
+ newInterval[0] = Math.min(newInterval[0], intervals[i][0]);
+ newInterval[1] = Math.max(newInterval[1], intervals[i][1]);
+ i++;
+ }
+ answer.add(newInterval);
+
+ // newInterval보다 오른쪽의 구간들 추가
+ while (i < n) {
+ answer.add(intervals[i]);
+ i++;
+ }
+
+ return answer.toArray(new int[answer.size()][]);
+ }
+}