2-g0rnn

g0rnn/README.md

@@ -1,6 +1,8 @@
-## ✏️ 기록   
+## ✏️ 기록
+
+| 차시  |    날짜    | 문제유형 |                                     링크                                     |                        풀이                        |
+| :---: | :--------: | :------: | :--------------------------------------------------------------------------: | :------------------------------------------------: |
+| 1차시 | 2024.10.01 |   DFS    | [타깃 넘버](https://school.programmers.co.kr/learn/courses/30/lessons/43165) | https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/4 |
+| 2차시 | 2024.10.03 |   트리   |   [LCA2](https://school.programmers.co.kr/learn/courses/30/lessons/176963)   | https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/7 |
 
-| 차시 |    날짜    | 문제유형 | 링크 | 풀이 |
-|:----:|:---------:|:----:|:-----:|:----:|
-| 1차시 | 2024.10.01 |  구현  | [추억 점수](https://school.programmers.co.kr/learn/courses/30/lessons/176963)|https://github.com/AlgoLeadMe/AlgoLeadMe-1/pull/35|
 ---

g0rnn/트리/2-g0rnn.java

@@ -0,0 +1,94 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+//TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or
+// click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.
+public class Main {
+    static final int MAX = 18; // 노드는 최대 100,000개
+    static int N, M;
+    static int[][] parent;
+    static int[] depth;
+    static List<Integer>[] adj;
+
+    // dfs를 사용하여 2차원 배열 parent를 초기화
+    public static void makeTree(int curNode) {
+        for (int child : adj[curNode]) {
+            if (depth[child] == -1) {
+                depth[child] = depth[curNode] + 1;
+                parent[child][0] = curNode;
+                makeTree(child);
+            }
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        //TIP Press <shortcut actionId="ShowIntentionActions"/> with your caret at the highlighted text
+        // to see how IntelliJ IDEA suggests fixing it.
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+
+        N = Integer.parseInt(br.readLine());
+        parent = new int[N][MAX];
+        depth = new int[N];
+        adj = new ArrayList[N];
+
+        for (int i = 0; i < N; i++) adj[i] = new ArrayList<>();
+
+        for (int i = 0; i < N - 1; i++) {
+            String[] input = br.readLine().split(" ");
+            int u = Integer.parseInt(input[0]) - 1;
+            int v = Integer.parseInt(input[1]) - 1;
+            adj[u].add(v);
+            adj[v].add(u);
+        }
+
+        for (int i = 0; i < N; i++) Arrays.fill(parent[i], -1);
+        Arrays.fill(depth, -1);
+        depth[0] = 0;
+
+        makeTree(0);
+
+        for (int j = 0; j < MAX - 1; j++) {
+            for (int i = 1; i < N; i++) {
+                if (parent[i][j] != -1)
+                    parent[i][j + 1] = parent[parent[i][j]][j];
+            }
+        }
+
+        M = Integer.parseInt(br.readLine());
+        for (int i = 0; i < M; i++) {
+            String[] nodePairs = br.readLine().split(" ");
+            int u = Integer.parseInt(nodePairs[0]) - 1;
+            int v = Integer.parseInt(nodePairs[1]) - 1;
+
+            if (depth[u] < depth[v]) {
+                int tmp = u;
+                u = v;
+                v = tmp;
+            }
+            int depthDiff = depth[u] - depth[v];
+
+            for (int j = 0; depthDiff > 0; j++) {
+                if (depthDiff % 2 == 1) u = parent[u][j];
+                depthDiff /= 2;
+            }
+
+            if (u != v) {
+                for (int j = MAX - 1; j >= 0; j--) {
+                    if(parent[u][j] != -1 && parent[u][j] != parent[v][j]) {
+                        u = parent[u][j];
+                        v = parent[v][j];
+                    }
+                }
+                u = parent[u][0];
+            }
+
+            System.out.println(u + 1);
+        }
+
+        br.close();
+    }
+}