From 8fead5831c963c489d7ca088f6ffca7c6cce5bb3 Mon Sep 17 00:00:00 2001 From: Tessa1217 Date: Mon, 23 Jun 2025 23:20:12 +0900 Subject: [PATCH 1/8] start new pull request --- meeting-rooms/Tessa1217.java | 2 ++ 1 file changed, 2 insertions(+) create mode 100644 meeting-rooms/Tessa1217.java diff --git a/meeting-rooms/Tessa1217.java b/meeting-rooms/Tessa1217.java new file mode 100644 index 000000000..046213d6a --- /dev/null +++ b/meeting-rooms/Tessa1217.java @@ -0,0 +1,2 @@ +public class Solution { +} From 1b735529f5d155da8ba87005ae96013e45cec60b Mon Sep 17 00:00:00 2001 From: Tessa1217 Date: Mon, 23 Jun 2025 23:40:47 +0900 Subject: [PATCH 2/8] add kth smallest element in a bst solution --- kth-smallest-element-in-a-bst/Tessa1217.java | 51 ++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 kth-smallest-element-in-a-bst/Tessa1217.java diff --git a/kth-smallest-element-in-a-bst/Tessa1217.java b/kth-smallest-element-in-a-bst/Tessa1217.java new file mode 100644 index 000000000..452fd995a --- /dev/null +++ b/kth-smallest-element-in-a-bst/Tessa1217.java @@ -0,0 +1,51 @@ +/** + * 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 { + + private int count = 0; + + private int kthSmallValue = 0; + + // 시간복잡도: O(k) (불균형 상태의 이진 트리일 경우 O(n)) + public int kthSmallest(TreeNode root, int k) { + orderSearch(root, k); + return kthSmallValue; + } + + // In Order Search + private void orderSearch(TreeNode node, int k) { + + if (node == null) { + return; + } + + // HINT => utilize the property of a BST => 좌측 리프 노드부터 탐색 + orderSearch(node.left, k); + + count++; + + if (count == k) { + kthSmallValue = node.val; + return; + } + + // search right side + orderSearch(node.right, k); + + } + +} + From 11c1853754bfd08cf6c482a7a7ce5b78bddbba5d Mon Sep 17 00:00:00 2001 From: Tessa1217 Date: Thu, 26 Jun 2025 20:47:09 +0900 Subject: [PATCH 3/8] add lowest common ancestor of a BST solution --- .../Tessa1217.java | 33 +++++++++++++++++++ 1 file changed, 33 insertions(+) create mode 100644 lowest-common-ancestor-of-a-binary-search-tree/Tessa1217.java diff --git a/lowest-common-ancestor-of-a-binary-search-tree/Tessa1217.java b/lowest-common-ancestor-of-a-binary-search-tree/Tessa1217.java new file mode 100644 index 000000000..cc5d2dfb2 --- /dev/null +++ b/lowest-common-ancestor-of-a-binary-search-tree/Tessa1217.java @@ -0,0 +1,33 @@ +/** + * 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) { + + if (root == null || root == p || root == q) { + return root; + } + + // 재귀로 좌측과 우측 탐색 + TreeNode left = lowestCommonAncestor(root.left, p, q); + + TreeNode right = lowestCommonAncestor(root.right, p, q); + + // 좌우 둘 다 null이 아니라면: 현재 root를 조상으로 하는 서브 트리에서 p와 q를 발견했음을 의미하므로 root가 공통 조상 + if (left != null && right != null) { + return root; + } else if (left != null) { + return left; + } else { + return right; + } + + } +} + From c59747e4c1d7600224ab9559357300d6bc556525 Mon Sep 17 00:00:00 2001 From: Tessa1217 Date: Thu, 26 Jun 2025 20:47:23 +0900 Subject: [PATCH 4/8] find median from data stream solution --- find-median-from-data-stream/Tessa1217.java | 46 +++++++++++++++++++++ 1 file changed, 46 insertions(+) create mode 100644 find-median-from-data-stream/Tessa1217.java diff --git a/find-median-from-data-stream/Tessa1217.java b/find-median-from-data-stream/Tessa1217.java new file mode 100644 index 000000000..ff717faf6 --- /dev/null +++ b/find-median-from-data-stream/Tessa1217.java @@ -0,0 +1,46 @@ +import java.util.PriorityQueue; + +class MedianFinder { + + // 작은 수 범위 저장하는 힙 + private PriorityQueue smallHeap; + + // 큰 수 범위 저장하는 힙 + private PriorityQueue largeHeap; + + public MedianFinder() { + smallHeap = new PriorityQueue<>((a, b) -> b - a); + largeHeap = new PriorityQueue<> ((a, b) -> a - b); + } + + public void addNum(int num) { + // 작은 수 범위에 삽입 + smallHeap.offer(num); + // 작은 수 범위에서 최댓값을 뽑아 큰 수 범위로 이동 + largeHeap.offer(smallHeap.poll()); + + // 만약 작은 수 범위의 개수가 큰 수 범위보다 작다면 + if (smallHeap.size() < largeHeap.size()) { + // 큰 수 범위에서 최솟값을 뽑아 작은 수 범위로 이동 + smallHeap.offer(largeHeap.poll()); + } + } + + public double findMedian() { + // 짝수 개일 경우 + if (smallHeap.size() == largeHeap.size()) { + // 작은 수 범위 힙의 최댓값 + 큰 수 범위 힙의 최솟값의 평균 + return (smallHeap.peek() + largeHeap.peek()) / 2.0; + } + // 작은 수 범위 힙의 최댓값 + return smallHeap.peek(); + } +} + +/** + * Your MedianFinder object will be instantiated and called as such: + * MedianFinder obj = new MedianFinder(); + * obj.addNum(num); + * double param_2 = obj.findMedian(); + */ + From 0948a7c76c2e7a4f1ffb400d171b5a7d056ff1eb Mon Sep 17 00:00:00 2001 From: Tessa1217 Date: Thu, 26 Jun 2025 20:58:22 +0900 Subject: [PATCH 5/8] add meeting rooms solution --- meeting-rooms/Tessa1217.java | 40 ++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) diff --git a/meeting-rooms/Tessa1217.java b/meeting-rooms/Tessa1217.java index 046213d6a..3ad8cf994 100644 --- a/meeting-rooms/Tessa1217.java +++ b/meeting-rooms/Tessa1217.java @@ -1,2 +1,42 @@ +import java.util.Collections; +import java.util.List; + +/** + * Definition of Interval: + * public class Interval { + * int start, end; + * Interval(int start, int end) { + * this.start = start; + * this.end = end; + * } + * } + */ + public class Solution { + /** + * @param intervals: an array of meeting time intervals + * @return: if a person could attend all meetings + */ + + // 시간복잡도: O(n log n) - 정렬, 공간복잡도: O(1) + public boolean canAttendMeetings(List intervals) { + // Write your code here + + if (intervals == null || intervals.isEmpty()) return true; + + Collections.sort(intervals, (i1, i2) -> i1.start - i2.start); + + Interval previous = intervals.get(0); + + for (int i = 1; i < intervals.size(); i++) { + Interval current = intervals.get(i); + if (previous.end > current.start) { + return false; + } + previous = current; + } + + return true; + } } + From 3551c6b4e53e41e38674df762e3c841e55484059 Mon Sep 17 00:00:00 2001 From: Tessa1217 Date: Fri, 27 Jun 2025 00:49:59 +0900 Subject: [PATCH 6/8] add insert interval solution --- insert-interval/Tessa1217.java | 39 ++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 insert-interval/Tessa1217.java diff --git a/insert-interval/Tessa1217.java b/insert-interval/Tessa1217.java new file mode 100644 index 000000000..8e14916ab --- /dev/null +++ b/insert-interval/Tessa1217.java @@ -0,0 +1,39 @@ +import java.util.ArrayList; +import java.util.List; + +class Solution { + + // 시간, 공간복잡도: O(n) + public int[][] insert(int[][] intervals, int[] newInterval) { + + // 병합된 interval 담는 list + List modifyIntervals = new ArrayList<>(); + + int idx = 0; + + // 병합 이전 구간 + while (idx < intervals.length && intervals[idx][1] < newInterval[0]) { + modifyIntervals.add(intervals[idx]); + idx++; + } + + // 병합이 필요한 구간 (newInterval과 겹치는 구간) + while (idx < intervals.length && intervals[idx][0] <= newInterval[1]) { + newInterval[0] = Math.min(intervals[idx][0], newInterval[0]); + newInterval[1] = Math.max(intervals[idx][1], newInterval[1]); + idx++; + } + + // 최종 병합된 새로운 interval add + modifyIntervals.add(newInterval); + + // 병합 이후 구간 + while (idx < intervals.length) { + modifyIntervals.add(intervals[idx]); + idx++; + } + + return modifyIntervals.toArray(new int[modifyIntervals.size()][2]); + } +} + From 6bd9e352089d78484c62ab4507d5562e2aab07df Mon Sep 17 00:00:00 2001 From: Tessa1217 <96612755+Tessa1217@users.noreply.github.com> Date: Wed, 2 Jul 2025 09:28:07 +0900 Subject: [PATCH 7/8] Create Tessa1217.java --- counting-bits/Tessa1217.java | 4 ++++ 1 file changed, 4 insertions(+) create mode 100644 counting-bits/Tessa1217.java diff --git a/counting-bits/Tessa1217.java b/counting-bits/Tessa1217.java new file mode 100644 index 000000000..230d82eb7 --- /dev/null +++ b/counting-bits/Tessa1217.java @@ -0,0 +1,4 @@ +class Solution { + +} + From fa8a8392a74dbe8bac580ad2960c4bf603db20d2 Mon Sep 17 00:00:00 2001 From: Tessa1217 <96612755+Tessa1217@users.noreply.github.com> Date: Wed, 2 Jul 2025 09:34:07 +0900 Subject: [PATCH 8/8] Delete counting-bits/Tessa1217.java --- counting-bits/Tessa1217.java | 4 ---- 1 file changed, 4 deletions(-) delete mode 100644 counting-bits/Tessa1217.java diff --git a/counting-bits/Tessa1217.java b/counting-bits/Tessa1217.java deleted file mode 100644 index 230d82eb7..000000000 --- a/counting-bits/Tessa1217.java +++ /dev/null @@ -1,4 +0,0 @@ -class Solution { - -} -