You are building a pyramid by stacking blocks, each represented by a color denoted by a letter. Each row above the bottom consists of one less block, centered on the row beneath. Only specific triangular patterns of blocks are allowed. A triangular pattern consists of three blocks: two at the bottom and one on top. Given the bottom row and allowed patterns, determine if it’s possible to construct the pyramid.
You are given an undirected graph where each node is labeled between 0 and n - 1. The graph is represented as a 2D array, where graph[u] contains the nodes that are adjacent to node u. A graph is bipartite if its nodes can be divided into two sets such that every edge connects a node from one set to a node in the other set. Your task is to return true if the graph is bipartite, otherwise return false.
You are given a number of cities and a list of flights between them. Each flight has a price and connects two cities. You need to find the cheapest route from a given source city to a destination city with at most a certain number of stops. If no such route exists, return -1.
You are given a directed acyclic graph (DAG) with n nodes, labeled from 0 to n-1. Find all possible paths from node 0 to node n-1 and return these paths in any order. The graph is represented such that each node has a list of other nodes that can be visited directly from it.
You are given a directed graph where each node represents a point, and edges represent possible transitions between nodes. A node is considered terminal if it has no outgoing edges. A node is deemed safe if every path starting from it leads either to a terminal node or another safe node. Your task is to identify all the safe nodes in the graph and return them in ascending order.
You are given the root of a binary tree. Your task is to remove all subtrees in the tree that do not contain at least one node with the value 1. A subtree is defined as the node and all its descendants. Return the modified tree.
