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] = [a_{i}, b_{i}]
indicates that you must take course b_{i}
first if you want to take course a_{i}
.
 For example, the pair
[0, 1]
, indicates that to take course0
you have to first take course1
.
Return true
if you can finish all courses. Otherwise, return false
.
Example 1:
Input: numCourses = 2, prerequisites = [[1,0]]
Output: true
Explanation: There are a total of 2 courses to take.
To take course 1 you should have finished course 0. So it is possible.
Example 2:
Input: numCourses = 2, prerequisites = [[1,0],[0,1]]
Output: false
Explanation: There are a total of 2 courses to take.
To take course 1 you should have finished course 0, and to take course 0
you should also have finished course 1. So it is impossible.
Constraints:
1 <= numCourses <= 2000
0 <= prerequisites.length <= 5000
prerequisites[i].length == 2
0 <= a_{i}, b_{i} < numCourses
 All the pairs
prerequisites[i]
are unique.

