LeetCode-in-All
207. Course Schedule
Medium
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 course0you 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 <= 20000 <= prerequisites.length <= 5000prerequisites[i].length == 20 <= ai, bi < numCourses- All the pairs prerequisites[i] are unique.
Solution
func canFinish(numCourses int, prerequisites [][]int) bool {
graph := map[int][]int{}
for _, edge := range prerequisites {
graph[edge[1]] = append(graph[edge[1]], edge[0])
}
indegree := make([]int, numCourses)
queue := []int{}
for i := 0; i < numCourses; i++ {
for _, v := range graph[i] {
indegree[v]++
}
}
for i := 0; i < numCourses; i++ {
if indegree[i] == 0 {
queue = append(queue, i)
}
}
visited := 0
for len(queue) > 0 {
node := queue[0]
queue = queue[1:]
visited++
for _, v := range graph[node] {
indegree[v]--
if indegree[v] == 0 {
queue = append(queue, v)
}
}
}
return visited == numCourses
}