207. Course Schedule - https://leetcode.com/problems/course-schedule/

courseSchedule.go

func canFinish(numCourses int, prerequisites [][]int) bool {
    next := Next(numCourses, prerequisites)
    pres := Pres(next)
    
    return check(next, pres, numCourses)
}

func Next(n int, prereq [][]int) [][]int {
    next := make([][]int,n)
    for _, pair := range prereq {
        next[pair[1]] = append(next[pair[1]], pair[0])
    }
    
    return next
}

func Pres(next [][]int) []int {
    pres := make([]int, len(next))
    for _, neighbors := range next {
        for _, n := range neighbors {
            pres[n]++
        }
    }
    return pres
}

func check(next [][]int, pres []int, numCourses int) bool {
    var i int
    var j int
    
    for i = 0; i < numCourses; i++ {
        for j = 0; j < numCourses; j++ {
            if pres[j] == 0 {
                break
            }
        }
        
        if j >= numCourses {
            return false
        }
        
        pres[j] = -1
        
        for _, c := range next[j] {
            pres[c]--
        }
    }
    return true
    
}