Leetcode Solutions

Question Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n), ans[i] is the number of 1‘s in the binary representation of i. Example 1: Input: n = 2 Output: [0,1,1] Explanation: 0 –> 0 1 –> 1 2 –> 10 Example 2: Input: n = 5 Output: [0,1,1,2,1,2] Explanation: 0 –> 0 1 –> 1 […]

Question Given the head of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return the reordered list. The first node is considered odd, and the second node is even, and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input.

Question Given an integer n, return true if it is a power of three. Otherwise, return false. An integer n is a power of three, if there exists an integer x such that n == 3x. Example 1: Input: n = 27 Output: true Explanation: 27 = 33 Example 2: Input: n = 0 Output: false Explanation: There is no x where 3x =

Question Given an integer array nums, return the length of the longest strictly increasing subsequence. A subsequence is a sequence that can be derived from an array by deleting some or no elements without changing the order of the remaining elements. For example, [3,6,2,7] is a subsequence of the array [0,3,1,6,2,2,7]. Example 1: Input: nums = [10,9,2,5,3,7,101,18] Output: 4 Explanation: The

Question Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a

Question The median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value and the median is the mean of the two middle values. For example, for arr = [2,3,4], the median is 3. For example, for arr = [2,3], the median is (2 + 3) / 2 =

Question You are playing the following Nim Game with your friend: Initially, there is a heap of stones on the table. You and your friend will alternate taking turns, and you go first. On each turn, the person whose turn it is will remove 1 to 3 stones from the heap. The one who removes the

Question Given a pattern and a string s, find if s follows the same pattern. Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in s. Example 1: Input: pattern = “abba”, s = “dog cat cat dog” Output: true Example 2: Input: pattern = “abba”, s = “dog cat cat fish” Output: false Example

Question Given an integer array nums, move all 0‘s to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0,1,0,3,12] Output: [1,3,12,0,0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <=

Question You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad. Suppose you have n versions [1, 2, …, n] and you want