문제 풀이 추가

Author: jinan159

src/제이/week11/BOJ_1068.java

@@ -0,0 +1,128 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.*;
+
+public class BOJ_1068 {
+
+    private static final int ROOT_INDEX = -1;
+
+    private static int removeTargetIndex;
+    private static final List<Node> nodes = new ArrayList<>();
+    private static List<Node> rootNodes = new ArrayList<>();
+
+    public static void main(String[] args) throws IOException {
+        readInput();
+        solve();
+    }
+
+    private static void solve() {
+        nodes.get(removeTargetIndex).disable();
+
+        int leafCount = findLeafCountDfs();
+
+        System.out.println(leafCount);
+    }
+
+    private static int findLeafCountDfs() {
+        int leafCount = 0;
+
+        Stack<Node> nodeStack = new Stack<>();
+
+        for (Node rootNode : rootNodes) {
+            if (rootNode.isActive()) {
+                nodeStack.add(rootNode);
+            }
+        }
+
+        while (!nodeStack.isEmpty()) {
+            Node node = nodeStack.pop();
+
+            if (node.isActive() && !node.hasChild()) {
+                leafCount++;
+                continue;
+            }
+
+            for (Node child : node) {
+                if (child.isActive()) {
+                    nodeStack.add(child);
+                }
+            }
+        }
+
+        return leafCount;
+    }
+
+    private static void readInput() throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        int nodeCount = Integer.parseInt(br.readLine());
+
+        for (int i = 0; i < nodeCount; i++) {
+            nodes.add(new Node(i));
+        }
+
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        for (int i = 0; i < nodeCount; i++) {
+            Node currentNode = nodes.get(i);
+
+            int parentIndex = Integer.parseInt(st.nextToken());
+            if (parentIndex == ROOT_INDEX) {
+                rootNodes.add(currentNode);
+                continue;
+            }
+
+            nodes.get(parentIndex).addChildNode(currentNode);
+        }
+
+        removeTargetIndex = Integer.parseInt(br.readLine());
+    }
+}
+
+class Node implements Iterable<Node> {
+    private final Set<Node> childs;
+    private final int index;
+    private boolean isActive = true;
+
+    public Node(int index) {
+        childs = new HashSet<>();
+        this.index = index;
+    }
+
+    public int getIndex() {
+        return index;
+    }
+
+    public boolean isActive() {
+        return isActive;
+    }
+
+    public void addChildNode(Node node) {
+        childs.add(node);
+    }
+
+    public boolean hasChild() {
+        if (childs.isEmpty()) {
+            return false;
+        }
+
+        for (Node child : childs) {
+            if (child.isActive()) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    public void disable() {
+        this.isActive = false;
+        childs.clear();
+    }
+
+    @Override
+    public Iterator<Node> iterator() {
+        return childs.iterator();
+    }
+}
+
+// 삽질1 : 2번째 줄에서 노드가 순서대로 나올 것이라고 생각했음