yejun614 · yejun614 · Feb 19, 2026 · Feb 19, 2026 · Feb 19, 2026 · Feb 19, 2026
diff --git a/problems/SWEA/p1238/Solution.java b/problems/SWEA/p1238/Solution.java
@@ -0,0 +1,129 @@
+/*
+ * (1238) [S/W 문제해결 기본] 10일차 - Contact
+ * https://swexpertacademy.com/main/code/problem/problemDetail.do?contestProbId=AV15B1cKAKwCFAYD&categoryId=AV15B1cKAKwCFAYD&categoryType=CODE&problemTitle=1238&orderBy=FIRST_REG_DATETIME&selectCodeLang=ALL&select-1=&pageSize=10&pageIndex=1
+ */
+
+import java.io.*;
+import java.util.*;
+
+/**
+ * SW Expert Academy - [S/W 문제해결 기본] 10일차 - Contact
+ * @author YeJun, Jung
+ * 
+ * [분석]
+ *   - BFS를 하는데, 마지막에 연락을 받는 노드들 중에서 가장 큰 숫자를 출력
+ * 
+ * [전략]
+ *   - BFS 사용
+ *   - visited 배열을 사용해서 방문 처리(양방향 통신이 가능한 경우를 처리하기 위함)
+ *   - 마지막에 연락을 받는 노드들 중에서 가장 큰 숫자를 출력
+ */
+public class Solution {
+  static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
+  static BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
+  static StringTokenizer input;
+
+  // ----------------------------------------------------------
+
+  public static void main(String[] args) throws IOException {
+    final int testCount = 10;
+
+    for (int testCase = 1; testCase <= testCount; testCase++) {
+      new Solution(testCase).run();
+    }
+  }
+
+  // ----------------------------------------------------------
+
+  static final int MAX_NODE_LEN = 101;
+
+  int testCase;
+  int answer;
+  int nodeLen;
+  int startNode;
+  List<List<Integer>> graph;
+  boolean[] visited;
+
+  public Solution(int testCase) {
+    this.testCase = testCase;
+  }
+
+  public void run() throws IOException {
+    input();
+    solve();
+    print();
+  }
+
+  private void input() throws IOException {
+    getLine();
+    nodeLen = Integer.parseInt(input.nextToken());
+    startNode = Integer.parseInt(input.nextToken());
+
+    int fromNode, toNode;
+    graph = new ArrayList<>(MAX_NODE_LEN);
+    for (int cnt = 0; cnt < MAX_NODE_LEN; cnt++) {
+      graph.add(new ArrayList<>());
+    }
+
+    getLine();
+    while (input.hasMoreTokens()) {
+      fromNode = Integer.parseInt(input.nextToken());
+      toNode = Integer.parseInt(input.nextToken());
+
+      graph.get(fromNode).add(toNode);
+    }
+  }
+
+  private void solve() {
+    visited = new boolean[MAX_NODE_LEN];
+    Deque<Context> q = new ArrayDeque<>();
+    answer = startNode;
+    int time = 0;
+
+    q.offer(new Context(startNode, time));
+    visited[startNode] = true;
+
+    while (!q.isEmpty()) {
+      Context peek = q.poll();
+
+      if (time == peek.time) {
+        answer = Math.max(answer, peek.node);
+      } else if (time < peek.time) {
+        answer = peek.node;
+        time = peek.time;
+      }
+
+      for (int node : graph.get(peek.node)) {
+        if (visited[node]) continue;
+        visited[node] = true;
+
+        q.offer(new Context(node, peek.time + 1));
+      }
+    }
+  }
+
+  private void print() throws IOException {
+    writer.write("#" + testCase);
+    writer.write(" " + answer);
+    writer.write("\n");
+    writer.flush();
+  }
+
+  // ----------------------------------------------------------
+
+  private static class Context {
+    int node;
+    int time;
+
+    public Context(int node, int time) {
+      this.node = node;
+      this.time = time;
+    }
+  }
+
+  // ----------------------------------------------------------
+
+  private static void getLine() throws IOException {
+    input = new StringTokenizer(reader.readLine().trim());
+  }
+}
diff --git a/problems/SWEA/p7733/Solution.java b/problems/SWEA/p7733/Solution.java
@@ -0,0 +1,144 @@
+/*
+ * (7733) 치즈 도둑
+ * https://swexpertacademy.com/main/code/problem/problemDetail.do?contestProbId=AWrDOdQqRCUDFARG&categoryId=AWrDOdQqRCUDFARG&categoryType=CODE&problemTitle=7733&orderBy=FIRST_REG_DATETIME&selectCodeLang=ALL&select-1=&pageSize=10&pageIndex=1
+ */
+
+import java.io.*;
+import java.util.*;
+
+/**
+ * SW Expert Academy - 치즈 도둑
+ * @author YeJun, Jung
+ * 
+ * [분석]
+ *   - 0...100일이 지나는 동안 매일 오늘 날짜에 해당하는 치즈가 삭제된다.
+ *   - 0일 최초의 치즈는 하나의 덩어리이다.
+ *   - 남아있는 치즈들이 상하좌우로 이웃해 있으면 하나의 그룹으로 본다.
+ * 
+ * [전략]
+ *   - 매일 해당 날짜의 치즈를 0으로 설정해 삭제 처리한다.
+ *     - 삭제한 치즈의 개수를 카운트해서 프로그램의 조기 종료를 가능하게 한다.
+ *   - 각 행렬 요소에 대해서 DFS를 하여 그룹의 개수를 센다.
+ *     - DFS할때 상하좌우로 이웃한 요소로 가지를 펼친다.
+ */
+public class Solution {
+  static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
+  static BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
+  static StringTokenizer input;
+
+  // ----------------------------------------------------------
+
+  public static void main(String[] args) throws IOException {
+    final int testCount = Integer.parseInt(reader.readLine().trim());
+
+    for (int testCase = 1; testCase <= testCount; testCase++) {
+      new Solution(testCase).run();
+    }
+  }
+
+  // ----------------------------------------------------------
+
+  static final int[] DIR_X = {  0,  0, -1,  1 };
+  static final int[] DIR_Y = { -1,  1,  0,  0 };
+  static final int DIR_LEN = 4;
+
+  int testCase;
+  int answer;
+  int boardSize;
+  int[][] board;
+  boolean[][] visited;
+
+  public Solution(int testCase) {
+    this.testCase = testCase;
+  }
+
+  public void run() throws IOException {
+    input();
+    solve();
+    print();
+  }
+
+  private void input() throws IOException {
+    boardSize = Integer.parseInt(reader.readLine().trim());
+    board = new int[boardSize][boardSize];
+
+    for (int y = 0; y < boardSize; y++) {
+      getLine();
+
+      for (int x = 0; x < boardSize; x++) {
+        board[y][x] = Integer.parseInt(input.nextToken());
+      }
+    }
+  }
+
+  private void solve() {
+    answer = 1; // 최초에 치즈는 하나의 덩어리이다.
+    int restBlocks = boardSize * boardSize;
+
+    for (int day = 1; day <= 100 && restBlocks > 0; day++) {
+      restBlocks -= eating(day);
+      answer = Math.max(answer, countGroup());
+    }
+  }
+
+  private int eating(int num) {
+    int eatCount = 0;
+
+    for (int y = 0; y < boardSize; y++) {
+      for (int x = 0; x < boardSize; x++) {
+        if (board[y][x] != num) continue;
+
+        board[y][x] = 0;
+        eatCount++;
+      }
+    }
+
+    return eatCount;
+  }
+
+  private int countGroup() {
+    visited = new boolean[boardSize][boardSize];
+    int result = 0;
+
+    for (int y = 0; y < boardSize; y++) {
+      for (int x = 0; x < boardSize; x++) {
+        if (dfs(x, y)) result++;
+      }
+    }
+
+    return result;
+  }
+
+  private boolean dfs(int x, int y) {
+    if (board[y][x] == 0 || visited[y][x]) return false;
+    visited[y][x] = true;
+
+    for (int dir = 0; dir < DIR_LEN; dir++) {
+      int nx = x + DIR_X[dir];
+      int ny = y + DIR_Y[dir];
+
+      if (!isInsideBoard(nx, ny)) continue;
+
+      dfs(nx, ny);
+    }
+
+    return true;
+  }
+
+  private boolean isInsideBoard(int x, int y) {
+    return x >= 0 && x < boardSize && y >= 0 && y < boardSize;
+  }
+
+  private void print() throws IOException {
+    writer.write("#" + testCase);
+    writer.write(" " + answer);
+    writer.write("\n");
+    writer.flush();
+  }
+
+  // ----------------------------------------------------------
+
+  private static void getLine() throws IOException {
+    input = new StringTokenizer(reader.readLine().trim());
+  }
+}
diff --git a/problems/baekjoon/p1987/Main.java b/problems/baekjoon/p1987/Main.java
@@ -0,0 +1,107 @@
+/*
+ * (1987) 알파벳
+ * https://www.acmicpc.net/problem/1987
+ */
+
+import java.io.*;
+import java.util.*;
+
+/**
+ * Baekjoon - 알파벳
+ * @author YeJun, Jung
+ * 
+ * [분석]
+ *   - 보드를 상하좌우로 이동하면서 방문한다.
+ *   - 방문한 곳에 있는 알파벳을 기억해 두었다가, 해당 알파벳이 적힌 다른 타일을 방문할 수 없다.
+ *   - 초기위치(0, 0)에 있는 알파벳에도 동일하게 적용된다.
+ * 
+ * [전략]
+ *   - DFS하면서 상하좌우 탐색한다.
+ *   - visitied 배열에 알파벳을 키로 하여 방문여부를 저장한다.
+ *   - 위치가 아닌 값을 이용해서 방문 처리하므로 DFS시 자식 노드 탐색 후 방문을 해제해 주어야 한다.
+ */
+public class Main {
+  static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
+  static BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
+  static StringTokenizer input;
+
+  // ----------------------------------------------------------
+
+  public static void main(String[] args) throws IOException {
+    new Main().run();
+  }
+
+  // ----------------------------------------------------------
+
+  static final int[] DIR_X = { -1,  1,  0,  0 };
+  static final int[] DIR_Y = {  0,  0, -1,  1 };
+  static final int DIR_LEN = 4;
+  static final int ALPHABET_LEN = 'Z' - 'A' + 1;
+
+  int answer;
+  int boardWidth;
+  int boardHeight;
+  char[][] board;
+  boolean[] visited;
+
+  public void run() throws IOException {
+    input();
+    solve();
+    print();
+  }
+
+  private void input() throws IOException {
+    getLine();
+    boardHeight = Integer.parseInt(input.nextToken());
+    boardWidth = Integer.parseInt(input.nextToken());
+
+    board = new char[boardHeight][];
+
+    for (int y = 0; y < boardHeight; y++) {
+      board[y] = reader.readLine().trim().toCharArray();
+    }
+  }
+
+  private void solve() {
+    visited = new boolean[ALPHABET_LEN];
+
+    visited[board[0][0] - 'A'] = true;
+    answer = dfs(0, 0);
+  }
+
+  private int dfs(int x, int y) {
+    int result = 0;
+
+    for (int dir = 0; dir < DIR_LEN; dir++) {
+      int nx = x + DIR_X[dir];
+      int ny = y + DIR_Y[dir];
+
+      if (!isInsideBoard(nx, ny)) continue;
+
+      char ch = board[ny][nx];
+      int key = ch - 'A';
+      if (visited[key]) continue;
+
+      visited[key] = true;
+      result = Math.max(result, dfs(nx, ny));
+      visited[key] = false;
+    }
+
+    return 1 + result;
+  }
+
+  private boolean isInsideBoard(int x, int y) {
+    return x >= 0 && x < boardWidth && y >= 0 && y < boardHeight;
+  }
+
+  private void print() throws IOException {
+    writer.write(answer + "\n");
+    writer.flush();
+  }
+
+  // ----------------------------------------------------------
+
+  private static void getLine() throws IOException {
+    input = new StringTokenizer(reader.readLine().trim());
+  }
+}