1 files changed, 60 insertions, 0 deletions
diff --git a/CourseSchedule.java b/CourseSchedule.java
new file mode 100644
index 0000000..5b5ed02
--- /dev/null
+++ b/CourseSchedule.java
@@ -0,0 +1,60 @@
+import java.lang.*;
+import java.util.*;
+import node.*;
+
+class CourseSchedule {
+	public static boolean canFinish(int[][] prerequisites) {
+		GraphNode node = createGraph(prerequisites);
+		return !detectCycle(node);
+	}
+
+	public static GraphNode createGraph(int[][] prerequisites) {
+		HashMap<Integer, GraphNode> map = new HashMap<Integer, GraphNode>();
+		for (int[] prerequisite : prerequisites) {
+			if (map.containsKey(prerequisite[0])) {
+				if (map.containsKey(prerequisite[1])) {
+					map.get(prerequisite[0]).neighbors.add(map.get(prerequisite[1]));
+				} else {
+					GraphNode node = new GraphNode(prerequisite[1]);
+					map.put(node.val, node);
+					map.get(prerequisite[0]).neighbors.add(node);
+				}
+				continue;
+			}
+			GraphNode pre = new GraphNode(prerequisite[1]);
+			GraphNode node = new GraphNode(prerequisite[0],
+					new ArrayList<GraphNode>(Arrays.asList(pre)));
+			map.put(pre.val, pre);
+			map.put(node.val, node);
+		}
+		// TODO: return first GraphNode in map
+		return map.get(1);
+	}
+
+	public static boolean detectCycle(GraphNode node) {
+		Stack<GraphNode> stack = new Stack<GraphNode>();
+		ArrayList<GraphNode> visited = new ArrayList<GraphNode>();
+		stack.push(node);
+		while (!stack.empty()) {
+			node = stack.pop();
+			if (visited.contains(node)) {
+				System.out.println("Cycle " + node.val);
+				return true;
+			}
+			visited.add(node);
+			System.out.println("Node: " + node.val);
+			System.out.print("Neighbors: ");
+			for (GraphNode neighbor : node.neighbors) {
+				stack.push(neighbor);
+				System.out.print(neighbor.val + " ");
+			}
+			System.out.println();
+		}
+		return false;
+	}
+
+	public static void main(String[] args) {
+		int[][] prerequisites = {{1, 4}, {1, 2}, {2, 3}, {3, 6}, {6, 2}, {4, 5}};
+		System.out.println(canFinish(prerequisites));
+	}
+}