g2101_2200.s2192_all_ancestors_of_a_node_in_a_directed_acyclic_graph

Class Solution

java.lang.Object

g2101_2200.s2192_all_ancestors_of_a_node_in_a_directed_acyclic_graph.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 Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
List<List<Integer>>	getAncestors(int n, int[][] edges)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Solution

public Solution()

Method Detail

getAncestors

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