Leetcode

![https://leetcode.com/problems/top-k-frequent-elements/] Given a non-empty array of integers, return the k most frequent elements. Example 1: Input: nums = [1,1,1,2,2,3], k = 2 Output: [1,2] Example 2: Input: nums = [1], k = 1 Output: [1] Note: You may assume k is always valid, 1 ≤ k ≤ number of unique elements. Your algorithm’s time complexity must be better than O(n log n), where n is the array’s size. It’s guaranteed that the answer is unique, in other words the set of the top k frequent elements is unique. You can return the answer in any order. class Solution { public int[] topKFrequent(int[] nums, int k) { List<Integer>[] buckets = new List[nums.length + 1]; Map<Integer, Integer> freq = new HashMap<>(); for (int num: nums) { freq.put(num, freq.getOrDefault(num, 0) + 1); } for (var entry: freq.entrySet()) { List<Integer> bucket = buckets[entry.getValue()]; if (bucket == null) { bucket = new ArrayList<>(); } bucket.add(entry.getKey()); buckets[entry.getValue()] = bucket; } int[] res = new int[k]; int j = 0; for (int i = buckets.length - 1; i >= 0 && j < k; i--) { if (buckets[i] != null) { for (Integer val : buckets[i]) { res[j++] = val; } } } return res; } public int[] topKFrequent2(int[] nums, int k) { Map<Integer, Integer> freq = new HashMap<>(); for (int num: nums) { freq.put(num, freq.getOrDefault(num, 0) + 1); } PriorityQueue<Map.Entry<Integer, Integer>> q = new PriorityQueue<>((e1, e2) -> e1.getValue() - e2.getValue()); for (Map.Entry<Integer, Integer> entry: freq.entrySet()) { q.add(entry); if (q.size() > k) { q.poll(); } System.out.println(q); } int[] res = new int[q.size()]; int i = 0; for (var entry: q) { res[i++] = entry.getKey(); } return res; } }

![https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/] Given an n x n matrix where each of the rows and columns are sorted in ascending order, return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order, not the kth distinct element. Example 1: Input: matrix = [[1,5,9],[10,11,13],[12,13,15]], k = 8 Output: 13 Explanation: The elements in the matrix are [1,5,9,10,11,12,13,13,15], and the 8th smallest number is 13 Example 2: Input: matrix = [[-5]], k = 1 Output: -5 Constraints: ...

![https://leetcode.com/problems/insert-interval/] Given a set of non-overlapping intervals, insert a new interval into the intervals (merge if necessary). You may assume that the intervals were initially sorted according to their start times. Example 1: Input: intervals = [[1,3],[6,9]], newInterval = [2,5] Output: [[1,5],[6,9]] Example 2: Input: intervals = [[1,2],[3,5],[6,7],[8,10],[12,16]], newInterval = [4,8] Output: [[1,2],[3,10],[12,16]] Explanation: Because the new interval [4,8] overlaps with [3,5],[6,7],[8,10]. Example 3: Input: intervals = [], newInterval = [5,7] Output: [[5,7]] Example 4: Input: intervals = [[1,5]], newInterval = [2,3] Output: [[1,5]] Example 5: Input: intervals = [[1,5]], newInterval = [2,7] Output: [[1,7]] Constraints: ...

Design a class to find the kth largest element in a stream. Note that it is the kth largest element in the sorted order, not the kth distinct element. Implement KthLargest class: KthLargest(int k, int[] nums) Initializes the object with the integer k and the stream of integers nums. int add(int val) Returns the element representing the kth largest element in the stream. Example 1: Input ["KthLargest", "add", "add", "add", "add", "add"] [[3, [4, 5, 8, 2]], [3], [5], [10], [9], [4]] Output [null, 4, 5, 5, 8, 8] Explanation KthLargest kthLargest = new KthLargest(3, [4, 5, 8, 2]); kthLargest.add(3); // return 4 kthLargest.add(5); // return 5 kthLargest.add(10); // return 5 kthLargest.add(9); // return 8 kthLargest.add(4); // return 8 Constraints: ...

![https://leetcode.com/problems/sort-the-matrix-diagonally/] A matrix diagonal is a diagonal line of cells starting from some cell in either the topmost row or leftmost column and going in the bottom-right direction until reaching the matrix’s end. For example, the matrix diagonal starting from mat[2][0], where mat is a 6 x 3 matrix, includes cells mat[2][0], mat[3][1], and mat[4][2]. Given an m x n matrix mat of integers, sort each matrix diagonal in ascending order and return the resulting matrix. ...

![https://leetcode.com/problems/sort-colors/] Given an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white, and blue. We will use the integers 0, 1, and 2 to represent the color red, white, and blue, respectively. Example 1: Input: nums = [2,0,2,1,1,0] Output: [0,0,1,1,2,2] Example 2: Input: nums = [2,0,1] Output: [0,1,2] Example 3: Input: nums = [0] Output: [0] Example 4: Input: nums = [1] Output: [1] Constraints: ...

![https://leetcode.com/problems/merge-intervals/] Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1,3],[2,6],[8,10],[15,18]] Output: [[1,6],[8,10],[15,18]] Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6]. Example 2: Input: intervals = [[1,4],[4,5]] Output: [[1,5]] Explanation: Intervals [1,4] and [4,5] are considered overlapping. Constraints: ...

![https://leetcode.com/problems/largest-values-from-labels/] We have a set of items: the i-th item has value values[i] and label labels[i]. Then, we choose a subset S of these items, such that: |S| <= num_wanted For every label L, the number of items in S with label L is <= use_limit. Return the largest possible sum of the subset S. Example 1: Input: values = [5,4,3,2,1], labels = [1,1,2,2,3], num_wanted = 3, use_limit = 1 Output: 9 Explanation: The subset chosen is the first, third, and fifth item. Example 2: Input: values = [5,4,3,2,1], labels = [1,3,3,3,2], num_wanted = 3, use_limit = 2 Output: 12 Explanation: The subset chosen is the first, second, and third item. Example 3: Input: values = [9,8,8,7,6], labels = [0,0,0,1,1], num_wanted = 3, use_limit = 1 Output: 16 Explanation: The subset chosen is the first and fourth item. Example 4: Input: values = [9,8,8,7,6], labels = [0,0,0,1,1], num_wanted = 3, use_limit = 2 Output: 24 Explanation: The subset chosen is the first, second, and fourth item. Note: ...

![https://leetcode.com/problems/search-a-2d-matrix-ii/] Write an efficient algorithm that searches for a target value in an m x n integer matrix. The matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1,4,7,11,15],[2,5,8,12,19],[3,6,9,16,22],[10,13,14,17,24],[18,21,23,26,30]], target = 5 Output: true Example 2: Input: matrix = [[1,4,7,11,15],[2,5,8,12,19],[3,6,9,16,22],[10,13,14,17,24],[18,21,23,26,30]], target = 20 Output: false Constraints: ...

![https://leetcode.com/problems/widest-vertical-area-between-two-points-containing-no-points/] Given n points on a 2D plane where points[i] = [xi, yi], Return the widest vertical area between two points such that no points are inside the area. A vertical area is an area of fixed-width extending infinitely along the y-axis (i.e., infinite height). The widest vertical area is the one with the maximum width. Note that points on the edge of a vertical area are not considered included in the area. ...