1558 Course Schedule Iv

Course Schedule IV

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 course 0 before you can take course 1.

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 <= 100
0 <= prerequisites.length <= (numCourses * (numCourses - 1) / 2)
prerequisites[i].length == 2
0 <= ai, bi <= numCourses - 1
ai != bi
All the pairs [ai, bi] are **unique**.
The prerequisites graph has no cycles.
1 <= queries.length <= 104
0 <= ui, vi <= numCourses - 1
ui != vi

class Solution:
    # Performs DFS and returns true if there's a path between src and target and false otherwise.
    def isPrerequisite(
        self, adjList: dict, visited: List[bool], src: int, target: int
    ) -> bool:
        visited[src] = True

        if src == target:
            return True

        for adj in adjList.get(src, []):
            if not visited[adj]:
                if self.isPrerequisite(adjList, visited, adj, target):
                    return True
        return False

    def checkIfPrerequisite(
        self,
        numCourses: int,
        prerequisites: List[List[int]],
        queries: List[List[int]],
    ) -> List[bool]:
        adjList = {i: [] for i in range(numCourses)}

        for edge in prerequisites:
            adjList[edge[0]].append(edge[1])

        result = []

        for query in queries:
            # Reset the visited array for each query
            visited = [False] * numCourses
            result.append(
                self.isPrerequisite(adjList, visited, query[0], query[1])
            )

        return result