You have to paint all the houses such that no two adjacent houses have the same color.
The cost of painting each house with a certain color is represented by an n x 3 cost matrix costs.
For example, costs[0][0] is the cost of painting house 0 with the color red; costs[1][2] is the cost of painting house 1 with color green, and so on.
Return the minimum cost to paint all houses.
There is a directed graph of n nodes with each node labeled from 0 to n - 1. The graph is represented by a 0-indexed 2D integer array graph where graph[i] is an integer array of nodes adjacent to node i, meaning there is an edge from node i to each node in graph[i].
A node is a terminal node if there are no outgoing edges. A node is a safe node if every possible path starting from that node leads to a terminal node (or another safe node).
Return an array containing all the safe nodes of the graph. The answer should be sorted in ascending order.
Example 1:
Input: graph = [[1,2],[2,3],[5],[0],[5],[],[]]
Output: [2,4,5,6]
Explanation: The given graph is shown above.
Nodes 5 and 6 are terminal nodes as there are no outgoing edges from either of them.
Every path starting at nodes 2, 4, 5, and 6 all lead to either node 5 or 6.Example 2:
Input: graph = [[1,2,3,4],[1,2],[3,4],[0,4],[]]
Output: [4]
Explanation: Only node 4 is a terminal node, and every path starting at node 4 leads to node 4.这道题其实混合了两个常见面试题方向：一类是“油漆房子”动态规划，核心是用状态转移避免相邻房子同色；另一类是“有向图中的安全节点”，通常用反向建图配合拓扑排序，或者用 DFS 三色标记判断节点是否会进入环。题面中给出了图的定义、终点节点与安全节点的含义，以及示例图中哪些节点最终会被判定为安全。做这类题时，重点是把“所有路径都能到达终点”转化为可验证的图算法条件。
