Leetcode

Problem Statement Description Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct. Examples Example 1: Input: nums = [1,2,3,1] Output: true Example 2: Input: nums = [1,2,3,4] Output: false Example 3: Input: nums = [1,1,1,3,3,4,3,2,4,2] Output: true Constraints 1 <= nums.length <= 105 -109 <= nums[i] <= 109 Key Insights This is a very simple problem that introduces the concept of a hash set....

Problem Statement Description Given the head of a singly linked list, return the middle node of the linked list. If there are two middle nodes, return the second middle node. Examples Example 1: flowchart LR a((1))-->b((2))-->c(3)-->d((4))-->e((5)) Input: head = [1,2,3,4,5] Output: [3,4,5] Explanation: The middle node of the list is node 3. Example 2: flowchart LR a((1))-->b((2))-->c((3))-->d(4)-->e((5))-->f((6)) Input: head = [1,2,3,4,5,6] Output: [4,5,6] Explanation: Since the list has two middle nodes with values 3 and 4, we return the second one....

Problem Statement Description Given the root of a binary tree, return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Examples Example 1: flowchart TD a((1))-->b((2)) b-->c((4)) b-->d((5)) a-->e((3)) Input: root = [1,2,3,4,5] Output: 3 Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3]....

Problem Statement Description Given an array nums of size n, return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Examples Example 1: Input: nums = [3,2,3] Output: 3 Example 2: Input: nums = [2,2,1,1,1,2,2] Output: 2 Constraints n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Key Insights There are many different ways to solve this problem....

Problem Statement Description Given the head of a singly linked list, reverse the list, and return the reversed list. Examples Example 1: Input: head = [1,2,3,4,5] Output: [5,4,3,2,1] Example 2: Input: head = [1,2] Output: [2,1] Example 3: Input: head = [] Output: [] Constraints The number of nodes in the list is the range [0, 5000] -5000 <= Node.val <= 5000 Key Insights In order to reverse a singly linked list iteratively, you need to use three pointers: prev, curr and next....