1462. Course Schedule IV
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There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course ai first if you want to take course bi.
- For example, the pair
[0, 1]indicates that you have to take course0before you can take course1.
Prerequisites can also be indirect. If course a is a prerequisite of course b, and course b is a prerequisite of course c, then course a is a prerequisite of course c.
You are also given an array queries where queries[j] = [uj, vj]. For the jth query, you should answer whether course uj is a prerequisite of course vj or not.
Return a boolean array answer, where answer[j] is the answer to the jth query.
Example 1:
Input: numCourses = 2, prerequisites = [[1,0]], queries = [[0,1],[1,0]] Output: [false,true] Explanation: The pair [1, 0] indicates that you have to take course 1 before you can take course 0. Course 0 is not a prerequisite of course 1, but the opposite is true.
Example 2:
Input: numCourses = 2, prerequisites = [], queries = [[1,0],[0,1]] Output: [false,false] Explanation: There are no prerequisites, and each course is independent.
Example 3:
Input: numCourses = 3, prerequisites = [[1,2],[1,0],[2,0]], queries = [[1,0],[1,2]] Output: [true,true]
Constraints:
2 <= numCourses <= 1000 <= prerequisites.length <= (numCourses * (numCourses - 1) / 2)prerequisites[i].length == 20 <= ai, bi <= numCourses - 1ai != bi- All the pairs
[ai, bi]are unique. - The prerequisites graph has no cycles.
1 <= queries.length <= 1040 <= ui, vi <= numCourses - 1ui != vi
Hints
Hint 1
Imagine if the courses are nodes of a graph. We need to build an array isReachable[i][j].
Hint 2
Start a bfs from each course i and assign for each course j you visit isReachable[i][j] = True.
Hint 3
Answer the queries from the isReachable array.