All Ancestors of a Node in a Directed Acyclic Graph
You are given a positive integer n representing the number of nodes of a Directed Acyclic Graph (DAG). The nodes are numbered from 0 to n - 1 (inclusive).
You are also given a 2D integer array edges, where edges[i] = [fromi, toi] denotes that there is a unidirectional edge from fromi to toi in the graph.
Return a list answer, where answer[i] is the list of ancestors of the i^th node, sorted in ascending order.
A node u is an ancestor of another node v if u can reach v via a set of edges.
Example 1
Input
n = 8, edges = [[0,3],[0,4],[1,3],[2,4],[2,7],[3,5],[3,6],[3,7],[4,6]]Output
[[],[],[],[0,1],[0,2],[0,1,3],[0,1,2,3,4],[0,1,2,3]]Nodes 0, 1, and 2 have no ancestors; each other node's list contains exactly the nodes that can reach it, sorted in ascending order.
Example 2
Input
n = 5, edges = [[0,1],[0,2],[0,3],[0,4],[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]Output
[[],[0],[0,1],[0,1,2],[0,1,2,3]]Node 0 has no ancestor, and each node i from 1 to 4 is reachable from all earlier nodes 0 through i - 1.
Constraints
- 1 <= n <= 1000
- 0 <= edges.length <= min(2000, n * (n - 1) / 2)
- edges[i].length == 2
- 0 <= fromi, toi <= n - 1
- fromi != toi
- There are no duplicate edges.
- The graph is directed and acyclic.