Dmitrii Volyx

253. Meeting Rooms II Given an array of meeting time intervals intervals where intervals[i] = [starti, endi], return the minimum number of conference rooms required. Example 1: Input: intervals = [[0,30],[5,10],[15,20]] Output: 2 Example 2: Input: intervals = [[7,10],[2,4]] Output: 1 Constraints: 1 <= intervals.length <= 10^4 0 <= starti < endi <= 10^6 Solution class Solution { /* [[0,30],[5,10],[15,20]] [ 0,30] [ 5,10] ---- [15,20] (1, 10), (2, 7), (3, 19), (8, 12), (10, 20), (11, 30) */ public int minMeetingRooms(int[][] intervals) { Arrays.sort(intervals, (a,b) -> a[0] - b[0]); PriorityQueue<int[]> pq = new PriorityQueue<int[]>((a,b) -> { return a[1] - b[1]; }); for (int[] interval: intervals) { if (!pq.isEmpty() && pq.peek()[1] <= interval[0]) { pq.poll(); } pq.add(interval); } return pq.size(); } } Solution 2 class Solution { public int minMeetingRooms(int[][] intervals) { Integer min = Integer.MAX_VALUE; Integer max = Integer.MIN_VALUE; for (int[] i: intervals) { min = Math.min(min, i[0]); max = Math.max(max, i[1]); } int[] times = new int[max - min + 1]; for (int[] i: intervals) { times[i[0] - min]++; times[i[1] - min]--; } int count = 0; int result = 0; for (int time: times) { count += time; result = Math.max(result, count); } return result; } }

314. Binary Tree Vertical Order Traversal Given the root of a binary tree, return the vertical order traversal of its nodes’ values. (i.e., from top to bottom, column by column). If two nodes are in the same row and column, the order should be from left to right. Example 1: Input: root = [3,9,20,null,null,15,7] Output: [[9],[3,15],[20],[7]] Example 2: Input: root = [3,9,8,4,0,1,7] Output: [[4],[9],[3,0,1],[8],[7]] Example 3: Input: root = [3,9,8,4,0,1,7,null,null,null,2,5] Output: [[4],[9,5],[3,0,1],[8,2],[7]] ...

987. Vertical Order Traversal of a Binary Tree Given the root of a binary tree, calculate the vertical order traversal of the binary tree. For each node at position (row, col), its left and right children will be at positions (row + 1, col - 1) and (row + 1, col + 1) respectively. The root of the tree is at (0, 0). The vertical order traversal of a binary tree is a list of top-to-bottom orderings for each column index starting from the leftmost column and ending on the rightmost column. There may be multiple nodes in the same row and same column. In such a case, sort these nodes by their values. ...

157. Read N Characters Given Read4 Given a file and assume that you can only read the file using a given method read4, implement a method to read n characters. Method read4: The API read4 reads four consecutive characters from file, then writes those characters into the buffer array buf4. The return value is the number of actual characters read. Note that read4() has its own file pointer, much like FILE *fp in C. ...

303. Range Sum Query - Immutable Given an integer array nums, handle multiple queries of the following type: Calculate the sum of the elements of nums between indices left and right inclusive where left <= right. Implement the NumArray class: NumArray(int[] nums) Initializes the object with the integer array nums. int sumRange(int left, int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + … + nums[right]). Example 1: Input ["NumArray", "sumRange", "sumRange", "sumRange"] [[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]] Output [null, 1, -1, -3] Explanation NumArray numArray = new NumArray([-2, 0, 3, -5, 2, -1]); numArray.sumRange(0, 2); // return (-2) + 0 + 3 = 1 numArray.sumRange(2, 5); // return 3 + (-5) + 2 + (-1) = -1 numArray.sumRange(0, 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3 Constraints: ...

1482. Minimum Number of Days to Make m Bouquets Given a string s, reverse only all the vowels in the string and return it. The vowels are ‘a’, ’e’, ‘i’, ‘o’, and ‘u’, and they can appear in both cases. Example 1: Input: s = "hello" Output: "holle" Example 2: Input: s = "leetcode" Output: "leotcede" Constraints: 1 <= s.length <= 3 * 105 s consist of printable ASCII characters. Solution class Solution { public String reverseVowels(String s) { Set<Character> vowels = new HashSet<>(); vowels.addAll(Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U')); int lo = 0; int hi = s.length() - 1; char[] word = s.toCharArray(); while (lo < hi) { while (lo < hi && !vowels.contains(word[lo])) { lo++; } while (lo < hi && !vowels.contains(word[hi])) { hi--; } char c = word[lo]; word[lo] = word[hi]; word[hi] = c; lo++; hi--; } return new String(word); } }

515. Find Largest Value in Each Tree Row Given the root of a binary tree, return an array of the largest value in each row of the tree (0-indexed). Example 1: Input: root = [1,3,2,5,3,null,9] Output: [1,3,9] Example 2: Input: root = [1,2,3] Output: [1,3] Example 3: Input: root = [1] Output: [1] Example 4: Input: root = [1,null,2] Output: [1,2] Example 5: Input: root = [] Output: [] ...

791. Custom Sort String You are given two strings order and s. All the words of order are unique and were sorted in some custom order previously. Permute the characters of s so that they match the order that order was sorted. More specifically, if a character x occurs before a character y in order, then x should occur before y in the permuted string. Return any permutation of s that satisfies this property. ...

977. Squares of a Sorted Array Given an integer array nums sorted in non-decreasing order, return an array of the squares of each number sorted in non-decreasing order. Example 1: Input: nums = [-4,-1,0,3,10] Output: [0,1,9,16,100] Explanation: After squaring, the array becomes [16,1,0,9,100]. After sorting, it becomes [0,1,9,16,100]. Example 2: Input: nums = [-7,-3,2,3,11] Output: [4,9,9,49,121] Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 nums is sorted in non-decreasing order. Follow up: Squaring each element and sorting the new array is very trivial, could you find an O(n) solution using a different approach? ...

1482. Minimum Number of Days to Make m Bouquets Given an integer array bloomDay, an integer m and an integer k. We need to make m bouquets. To make a bouquet, you need to use k adjacent flowers from the garden. The garden consists of n flowers, the ith flower will bloom in the bloomDay[i] and then can be used in exactly one bouquet. Return the minimum number of days you need to wait to be able to make m bouquets from the garden. If it is impossible to make m bouquets return -1. ...