order and str are strings composed of lowercase letters. In order, no letter occurs more than once. order was sorted in some custom order previously. We want to permute the characters of str so that t

Given a string s, return the number of unique palindromes of length three that are a subsequence of s. Note that even if there are multiple ways to obtain the same subsequence, it is still only counte

You are given two m x n binary matrices grid1 and grid2 containing only 0’s (representing water) and 1’s (representing land). An island is a group of 1’s connected 4-directionally (horizontal or verti

Given two n x n binary matrices mat and target, return true if it is possible to make mat equal to target by rotating mat in 90-degree increments, or false otherwise. Example 1: Input: mat = [[0,

Given a string s and an integer k, return true if you can use all the characters in s to construct k palindrome strings or false otherwise. Example 1:Input: s = “annabelle”, k = 2Output: tru

Given an array of integers arr, replace each element with its rank. The rank represents how large the element is. The rank has the following rules: Rank is an integer starting from 1. The larger the

You are given an integer array heights representing the heights of buildings, some bricks, and some ladders. You start your journey from building 0 and move to the next building by possibly using bric

There is a hidden integer array arr that consists of n non-negative integers. It was encoded into another integer array encoded of length n - 1, such that encoded[i] = arr[i] XOR arr[i + 1]. For

Given a binary array nums and an integer goal, return the number of non-empty subarrays with a sum goal. A subarray is a contiguous part of the array. Example 1:Input: nums = [1,0,1,0,1], goal &#

Design a system that manages the reservation state of n seats that are numbered from 1 to n. Implement the SeatManager class: SeatManager(int n) Initializes a SeatManager object that will manage n se