[20260123] BOJ / G4 / 트리 순 / 이인희

LiiNi-coder/202601/23 BOJ 트리 순회.md

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+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.Map;
+
+public class Main{
+
+	private static class Node{
+		int value;
+		Node c1;
+		Node c2;
+		public Node(int v){
+			this.value = v;
+			c1 = c2 = null;
+		}
+	}
+	private static Map<Integer, Node> Nodes;
+	private static long answer = 0;
+	private static Deque<Integer>  q = new ArrayDeque<>();
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		int n = Integer.parseInt(br.readLine());
+		int t = n;
+		Nodes = new HashMap<>();
+		Nodes.put(1, new Node(1));
+		while(t-->0){
+			String[] tokens = br.readLine().split(" ");
+			int parentValue = Integer.parseInt(tokens[0 ]);
+			Node parentNode = Nodes.get(parentValue);
+			if(parentNode == null){
+				parentNode = new Node(parentValue);
+				Nodes.put(parentValue, parentNode);
+			}
+
+			int child1Value = Integer.parseInt(tokens[1]);
+			if(child1Value != -1){
+				Node child1Node = Nodes.get(child1Value);
+				if(child1Node == null){
+					child1Node = new Node(child1Value);
+					Nodes.put(child1Value, child1Node);
+				}
+				parentNode.c1 = child1Node;
+			}
+			int child2Value = Integer.parseInt(tokens[2 ]);
+			if(child2Value != -1){
+				Node child2Node = Nodes.get(child2Value);
+				if(child2Node == null){
+					child2Node = new Node(child2Value);
+					Nodes.put(child2Value, child2Node);
+				}
+				parentNode.c2 = child2Node;
+			}
+		}
+		findLastNode(Nodes.get(1));
+		answer--;
+		dfs(Nodes.get(1));
+		br.close();
+	}
+
+	private static void dfs(Node cur) {
+		answer++;
+		if(cur.c1 != null){
+			dfs(cur.c1);
+			answer++;
+		}
+		if(q.getLast() == cur.value){
+			System.out.println(answer++);
+			System.exit(0);
+		}
+		if(cur.c2 != null){
+			dfs(cur.c2);
+			answer++;
+		}
+	}
+
+	private static void findLastNode(Node cur) {
+		if(cur.c1 != null){
+			findLastNode(cur.c1);
+		}
+		q.offerLast(cur.value);
+		if(cur.c2 != null){
+			findLastNode(cur.c2);
+		}
+	}
+}
+```