Velut arbor aevo.
Given an arrayContinue reading “[Leetcode]15. 3Sum”numsof n integers, are there elements a, b, c innumssuch that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. Note: The solution set must not contain duplicate triplets. Example: Given array nums = [-1, 0, 1, 2, -1, -4], A solution set is: [ [-1, 0, 1], [-1, -1, 2] ]
Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input would have exactly one solution, and you may not use the same element twice. Example: Given nums = [2, 7, 11, 15], target = 9, Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].Continue reading “[Leetcode]1. Two Sum”
Given an array of integersContinue reading “[Leetcode]1498. Number of Subsequences That Satisfy the Given Sum Condition”numsand an integertarget. Return the number of non-empty subsequences ofnumssuch that the sum of the minimum and maximum element on it is less or equal thantarget. Since the answer may be too large, return it modulo 10^9 + 7. Input: nums = [3,3,6,8], target = 10 Output: 6 Explanation: There are 6 subsequences that satisfy the condition. (nums can have repeated numbers). [3] , [3] , [3,3], [3,6] , [3,6] , [3,3,6]
Given an array of integersContinue reading “[Leetcode]1497. Check If Array Pairs Are Divisible by k”arrof even lengthnand an integerk. We want to divide the array into exactlyn / 2pairs such that the sum of each pair is divisible byk. Return True If you can find a way to do that or False otherwise. Example 1: Input: arr = [1,2,3,4,5,10,6,7,8,9], k = 5 Output: true Explanation: Pairs are (1,9),(2,8),(3,7),(4,6) and (5,10).
The cycle detection problem is to find the cycle in a sequence, and Floyd’s cycle detection algorithm, aka Tortoise and Hare algorithm, is a two pointers algorithm to detect the cycle and the start of the cycle as well.
Continue reading “Floyd’s Cycle Detection Algorithm – [Leetcode]142. Linked List Cycle II”
There are 8 prison cells in a row, and each cell is either occupied or vacant. Each day, whether the cell is occupied or vacant changes according to the following rules: 1. If a cell has two adjacent neighbors that are both occupied or both vacant, then the cell becomes occupied. 2. Otherwise, it becomes vacant. (Note that because the prison is a row, the first and the last cells in the row can't have two adjacent neighbors.) We describe the current state of the prison in the following way:Continue reading “[Leetcode]957. Prison Cells After N Days”cells[i] == 1if thei-th cell is occupied, elsecells[i] == 0. Given the initial state of the prison, return the state of the prison afterNdays (andNsuch changes described above.)
Given a 2D board and a list of words from the dictionary, find all words in the board. Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example: Input: board = [ ['o','a','a','n'], ['e','t','a','e'], ['i','h','k','r'], ['i','f','l','v'] ] words =Continue reading “[Leetcode]212. Word Search II”["oath","pea","eat","rain"]Output:["eat","oath"]
A trie, or a prefix tree, refers to an ordered data structure that is usually used to store strings (Wikipedia). The picture on the above is an example where a trie stores [ape,apple,are,art]. Now let’s take a closer look at it and it’s not hard to find that: