LeetCode 207. Course Schedule

public boolean canFinish(int numCourses, int[][] nums) {
ArrayList<GraphNode> graph = new ArrayList<>();
int[] visit = new int[numCourses];

for(int i = 0; i < numCourses; i++) {
graph.add(new GraphNode(i));
}

for(int i = 0; i < nums.length; i++) {
graph.get(nums[i][0]).neighbors.add(graph.get(nums[i][1]));
}

for(int i = 0; i < graph.size(); i++) {
if(visit[i] == 0 && !DFS(graph.get(i), visit)) {		//未访问且访问时遇到环
return false;
}
}

return true;
}

public boolean DFS(GraphNode node, int[] visit) {
visit[node.label] = 1;			//正在访问

for(int i = 0; i < node.neighbors.size(); i++) {
if(visit[node.neighbors.get(i).label] == 0) {
if(!DFS(node.neighbors.get(i), visit)) {
return false;
}
} else if(visit[node.neighbors.get(i).label] == 1) {
return false;
}
}

visit[node.label] = 2;			//访问过
return true;
}