Course Schedule

Medium~20 min

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 bi first if you want to take course ai.

For example, the pair [0, 1] indicates that to take course 0 you have to first take course 1.

Return true if you can finish all courses. Otherwise, return false.

Examples

Example 1
Input: numCourses = 2, prerequisites = [[1, 0]]
Output: true
Explanation: There are 2 courses. To take course 1 you must first take course 0. This is possible.
Example 2
Input: numCourses = 2, prerequisites = [[1, 0], [0, 1]]
Output: false
Explanation: There are 2 courses. Course 1 requires course 0, and course 0 requires course 1. This is a cycle, so it is impossible.

Constraints

  • 1 <= numCourses <= 2000
  • 0 <= prerequisites.length <= 5000
  • prerequisites[i].length == 2
  • 0 <= ai, bi < numCourses
  • All the pairs prerequisites[i] are unique
  • Expected time complexity: O(V + E)
Code
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Output

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