Difficulty/Medium

Problem Follow up for Remove duplicates from Sorted Array I: What if duplicates are allowed at most twice? OR Given an integer array nums sorted in non-decreasing order, remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same. Since it is impossible to change the length of the array in some languages, you must instead have the result be placed in the first part of the array nums. More formally, if there are k elements after removing the duplicates, then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements. ...

Problem You are given an m x n integer array grid. There is a robot initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m-1][n-1]). The robot can only move either down or right at any point in time. An obstacle and space are marked as 1 or 0 respectively in grid. A path that the robot takes cannot include any square that is an obstacle. ...

Problem Given the head of a linked list, rotate the list to the right by k places. Examples Example 1: Input: head = [1,2,3,4,5], k = 2 Output: [4,5,1,2,3] Example 2: Input: head = [0,1,2], k = 4 Output: [2,0,1] ...

Problem Given a positive integer n, generate an n x n matrix filled with elements from 1 to n2 in spiral order. Examples Example 1: Input: n = 3 Output: [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ] Example 2: Input: n = 4 Output: [ [1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7] ] ...

Problem Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input. OR Given a list of intervals, merge all the overlapping intervals to produce a list that has only mutually exclusive intervals. Examples Example 1: Input: intervals = [1,3],[2,6],[8,10],[15,18], Output: [1,6],[8,10],[15,18]. ...

Problem Given an array of strings strs, group the anagrams together. You can return the answer in any order. Definition Anagram Definition Examples For example, suppose that we have the following strings: Example 1: Input: strs = ["eat","tea","tan","ate","nat","bat"] Output: [ ["bat"],["nat","tan"],["ate","eat","tea"] ] ...

Problem Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Examples Example 1: Input: candidates = [10,1,2,7,6,1,5], target = 8 Output: [ [1,1,6], [1,2,5], [1,7], [2,6] ] ...

Problem Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. It is guaranteed that the number of unique combinations that sum up to target is less than 150 combinations for the given input. ...

Problem Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value. If target is not found in the array, return [-1, -1]. You must write an algorithm with O(log n) runtime complexity. Examples Example 1: Input: nums = [5,7,7,8,8,10], target = 8 Output: [3,4] ...

Problem Suppose a sorted array is rotated at some pivot unknown to you beforehand. (i.e., [0, 1, 2, 4, 5, 6, 7] might become [4, 5, 6, 7, 0, 1, 2]). You are given a target value to search. If found in the array return its index, otherwise return -1. You may assume no duplicate exists in the array. Follow up: what if duplicates are allowed? ...