Package g2101_2200.s2192_all_ancestors_of_a_node_in_a_directed_acyclic_graph

Class Solution

  • public class Solution
extends Object
    2192 - All Ancestors of a Node in a Directed Acyclic Graph.

    Medium

    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 ith 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, 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.

    Example 2:

    Input: n = 5, edgeList = [[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]]

    Explanation:

    The above diagram represents the input graph.

    • Node 0 does not have any ancestor.

    • Node 1 has one ancestor 0.

    • Node 2 has two ancestors 0 and 1.

    • Node 3 has three ancestors 0, 1, and 2.

    • Node 4 has four ancestors 0, 1, 2, and 3.

    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.

    • Constructor Detail

      • Solution

        public Solution()

    • Method Detail

      • getAncestors

        public List<List<Integer>> getAncestors​(int n,
                                        int[][] edges)