All Ancestors of a Node in a Directed Acyclic Graph

Difficulty

Medium

Question

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.

You are also given a 2D integer array edges where edges[i] = [from_i, to_i] denotes that there is a unidirectional edge from_i to to_i in the graph.

Return a list answer, where answer[i] is a 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:

Input: n = 8, edgeList = [[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]]
Explanation:
The above diagram represents the input graph.
- Nodes 0, 1, and 2 do not have any ancestors.
- Node 3 has two ancestors 0 and 1.
- Node 4 has two ancestors 0 and 2.
- Node 5 has three ancestors 0, 1, and 3.
- Node 6 has five ancestors 0, 1, 2, 3, and 4.
- Node 7 has four ancestors 0, 1, 2, and 3.

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Link

All Ancestors of a Node in a Directed Acyclic Graph