g0201_0300.s0207_course_schedule.Solution.kt Maven / Gradle / Ivy

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Kotlin-based LeetCode algorithm problem solutions, regularly updated

There is a newer version: 1.30

package g0201_0300.s0207_course_schedule

// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Depth_First_Search
// #Breadth_First_Search #Graph #Topological_Sort #Big_O_Time_O(N)_Space_O(N)
// #2024_01_16_Time_183_ms_(92.07%)_Space_39.1_MB_(81.50%)

class Solution {
    fun canFinish(numCourses: Int, prerequisites: Array): Boolean {
        val adj: Array> = Array(numCourses) { ArrayList() }
        for (pre in prerequisites) {
            adj[pre[1]].add(pre[0])
        }
        val colors = IntArray(numCourses)
        for (i in 0 until numCourses) {
            if (colors[i] == WHITE && adj[i].isNotEmpty() && hasCycle(adj, i, colors)) {
                return false
            }
        }
        return true
    }

    private fun hasCycle(adj: Array>, node: Int, colors: IntArray): Boolean {
        colors[node] = GRAY
        for (nei in adj[node]) {
            if (colors[nei] == GRAY) {
                return true
            }
            if (colors[nei] == WHITE && hasCycle(adj, nei, colors)) {
                return true
            }
        }
        colors[node] = BLACK
        return false
    }

    companion object {
        private const val WHITE = 0
        private const val GRAY = 1
        private const val BLACK = 2
    }
}