Build a Quadtree and Analyze a Graph

Solve the following two coding problems. 1. **Build a quadtree from an image** You are given an `N x N` matrix of integers representing an image, where `N` is a power of 2. A quadtree node represents a square region of the image. - If all values in the region are the same, the node should be a **leaf** storing that value. - Otherwise, the node should be an **internal node** with exactly four children representing the region's: - top-left quadrant - top-right quadrant - bottom-left quadrant - bottom-right quadrant Design the quadtree node structure and write a function that builds the quadtree for the input matrix. 2. **Find nodes that always lead to terminal nodes** You are given a directed graph with nodes labeled from `0` to `n - 1`, represented as an adjacency list `graph`, where `graph[i]` contains all outgoing neighbors of node `i`. - A **terminal node** is a node with no outgoing edges. - A node is **safe** if every possible path starting from that node eventually ends at a terminal node. Return all safe nodes in ascending order.