땃쥐 - BOJ_1068 (트리)

Author: ttasjwi

src/땃쥐/BOJ_1068.java

@@ -0,0 +1,128 @@
+package 땃쥐;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+public class BOJ_1068 {
+
+    private static int N; // 노드의 갯수
+    private static Node[] nodes;
+
+    public static void main(String[] args) throws IOException {
+        N = readInt();
+
+        nodes = new Node[N];
+
+        for (int i = 0; i < N; i++) {
+            nodes[i] = new Node(i);
+        }
+
+        for (int i = 0; i < N; i++) {
+            int parentNodeNumber = readInt();
+            if (isNotRootNode(parentNodeNumber)) {
+                nodes[parentNodeNumber].addChild(nodes[i]);
+            }
+        }
+
+        int deleteNodeNumber = readInt();
+        nodes[deleteNodeNumber].detach();
+
+        int count = 0;
+
+        for (Node node : nodes) {
+            if (node.isLeafNode()) {
+                count++;
+            }
+        }
+
+        System.out.print(count);
+    }
+
+    private static boolean isNotRootNode(int parentNodeNumber) {
+        return parentNodeNumber != -1;
+    }
+
+    private static int readInt() throws IOException {
+        int value = 0;
+        boolean negative = false;
+
+        int input;
+        while (true) {
+            input = System.in.read();
+            if (input == ' ' || input == '\n') {
+                return (negative) ? -value : value;
+            } else if (input == '-') {
+                negative = true;
+            } else {
+                value = value * 10 + (input - 48);
+            }
+        }
+    }
+}
+
+class Node {
+    Node parent;
+    List<Node> childs = new ArrayList<>();
+
+    final int value;
+    boolean detached;
+
+    public Node(int value) {
+        this.value = value;
+    }
+
+    public int getValue() {
+        return value;
+    }
+
+    public void addChild(Node child) { // 양방향 참조
+        childs.add(child);
+        child.parent = this;
+    }
+
+    public Node getRootNode() {
+        if (parent == null) {
+            return this;
+        }
+        Node parent = this.parent;
+
+        while(true) {
+            if (parent.parent == null) {
+                return parent;
+            }
+            parent = parent.parent;
+        }
+    }
+
+    public void detach() {
+        if (parent != null) {
+            parent.childs.remove(this);
+            this.parent = null;
+        }
+        detached = true;
+    }
+
+    public boolean isLeafNode() {
+        return !isRootDetached() && (childs.size() == 0);
+    }
+
+    public boolean isRootDetached() {
+        return getRootNode().detached;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Node node = (Node) o;
+        return getValue() == node.getValue();
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getValue());
+    }
+
+}