leetcode questions

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining. Input: height = [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. CPP solution … Read more

Given the root of a binary tree, determine if it is a valid binary search tree (BST). A valid BST is defined as follows: Input: root = [2,1,3] Output: true Solution : Java DFS : Python : CPP : Inorder solution :

Two integer arrays, nums and multipliers, of sizes n and m, respectively, are provided to you, where n >= m. The arrays are all one-dimensional. You start with a score of zero. You need to carry out precisely m operations. On the ith (1-indexed) action, you will: Choose one integer x from the beginning or … Read more

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1,0,1,2,-1,-4] Output: [[-1,-1,2],[-1,0,1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + … Read more

Given a string s, return the longest palindromic substring in s. A string is called a palindrome string if the reverse of that string is the same as the original string. Example 1: Input: s = “babad” Output: “bab” Explanation: “aba” is also a valid answer. Example 2: Input: s = “cbbd” Output: “bb” Solution : JavaScript : CPP … Read more

Find the length of the longest substring without repeated characters given a string s. Example 1: Input: s = “abcabcbb” Output: 3 Explanation: The answer is “abc”, with the length of 3. Example 2: Input: s = “bbbbb” Output: 1 Explanation: The answer is “b”, with the length of 1. Example 3: Input: s = … Read more

You are given two non-empty linked lists that each represent a non-negative integer. The digits are kept in reverse order, with each node containing only one digit. Add the two numbers together and return the total as a linked list. Except for the number 0 itself, you may presume that the two numbers do not … Read more

Provide the median of the two sorted arrays given two sorted arrays of sizes m and n, respectively. The entire complexity of the run time should be O(log (m+n)). Eg 1: Numbers1 = [1,3], Numbers2 = [2] Result: 2.00000 Explanation: the merged array equals [1,2,3], and the median is 2. Eg 2: Numbers1 = [1,2], … Read more

Sure, let’s solve the “Two Sum” problem using different approaches in C++, Python, Java, and JavaScript, and add some humor along the way! We’ll explore the bruteforce, hashmap, two hashmap, and two-pointer methods for each language. Time Complexity: C++: 1. Brute Force Approach: Notice: This approach has a time complexity of O(n^2), which isn’t very … Read more

Given the head of a linked list, return the node where the cycle begins. If there is no cycle, return null. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally, pos is used to denote the index of the node that tail’s next pointer is connected … Read more

Given the root of a binary tree, determine if it is a valid binary search tree (BST). A valid BST is defined as follows: Example 1: Input: root = [2,1,3] Output: true Solution

Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]). Return the running sum of nums. Example 1: Input: nums = [1,2,3,4] Output: [1,3,6,10] Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4]. Example 2: Input: nums = [1,1,1,1,1] Output: [1,2,3,4,5] Explanation: Running sum is obtained as follows: [1, 1+1, … Read more