11주차 일일 문제풀이

src/jaehoon/_11주차/BOJ_11655_ROT13.java

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+package jaehoon._11주차;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+// https://www.acmicpc.net/problem/11655
+public class BOJ_11655_ROT13 {
+
+  public static void main(String[] args) throws IOException {
+    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    String str = br.readLine();
+
+    StringBuilder st = new StringBuilder();
+    for (char ch : str.toCharArray()) {
+      if (Character.isLetter(ch)) {
+        st.append(ROT13(ch));
+        continue;
+      }
+      st.append(ch);
+    }
+    System.out.println(st);
+    br.close();
+  }
+
+  static char ROT13(char ch) {
+    if (Character.isUpperCase(ch)) {
+      return (char) ((ch - 'A' + 13) % 26 + 'A');
+    } else {
+      return (char) ((ch - 'a' + 13) % 26 + 'a');
+    }
+  }
+}

src/jaehoon/_11주차/BOJ_14502_연구소.java

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+package jaehoon._11주차;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayDeque;
+import java.util.StringTokenizer;
+
+public class BOJ_14502_연구소 {
+
+  private static int[] dy = {-1, 0, 1, 0};
+  private static int[] dx = {0, 1, 0, -1};
+  private static int[][] map;
+  private static int N;
+  private static int M;
+  private static ArrayDeque<Node> virus = new ArrayDeque<>();
+
+  private static class Node {
+    int r;
+    int c;
+
+    public Node(int r, int c) {
+      this.r = r;
+      this.c = c;
+    }
+  }
+
+  // 입력예시:
+  // 7 7
+  // 2 0 0 0 1 1 0
+  // 0 0 1 0 1 2 0
+  // 0 1 1 0 1 0 0
+  // 0 1 0 0 0 0 0
+  // 0 0 0 0 0 1 1
+  // 0 1 0 0 0 0 0
+  // 0 1 0 0 0 0 0
+  //
+  // 출력예시:
+  // 27
+  //
+  public static void main(String[] args) throws IOException {
+    // 입력 받기
+    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    StringTokenizer st = new StringTokenizer(br.readLine());
+    N = Integer.parseInt(st.nextToken());
+    M = Integer.parseInt(st.nextToken());
+
+    map = new int[N][M];
+    for (int i = 0; i < N; i++) {
+      st = new StringTokenizer(br.readLine());
+      for (int j = 0; j < M; j++) {
+        map[i][j] = Integer.parseInt(st.nextToken());
+        if (map[i][j] == 2) {
+          virus.addLast(new Node(i, j));
+        }
+      }
+    }
+
+    int answer = 0;
+
+    ArrayDeque<Node> wall = new ArrayDeque<>();
+    // 벽을 세울 수 있는 빈칸의 조합을 만듬 (3칸)
+    // 조합 생성 시 빈 칸만 탐색하므로, map[i][j] == 0인 칸들을 리스트 wall에 저장 - [i / M]하면 행의 위치, [i % M]하면 열의 위치
+    for (int i = 0; i < N * M - 2; i++) {
+      if (map[i / M][i % M] != 0) {
+        continue;
+      }
+      wall.addLast(new Node(i / M, i % M));
+      for (int j = i + 1; j < N * M - 1; j++) {
+        if (map[j / M][j % M] != 0) {
+          continue;
+        }
+        wall.addLast(new Node(j / M, j % M));
+        for (int k = j + 1; k < N * M; k++) {
+          if (map[k / M][k % M] != 0) {
+            continue;
+          }
+          wall.addLast(new Node(k / M, k % M));
+          // 조합을 가지고 bfs 탐색
+          answer = Math.max(answer, bfs(wall));
+          wall.pollLast();
+        }
+        wall.pollLast();
+      }
+      wall.pollLast();
+    }
+
+    System.out.println(answer);
+    br.close();
+  }
+
+  private static int bfs(ArrayDeque<Node> wall) {
+    // 맵을 복사해서 벽을 세우고, 바이러스를 전염시킬 것임
+    int[][] cMap = new int[N][M];
+    for (int i = 0; i < N; i++) {
+      for (int j = 0; j < M; j++) {
+        cMap[i][j] = map[i][j];
+      }
+    }
+
+    // 벽(1) 3개를 세움
+    for (Node node : wall) {
+      cMap[node.r][node.c] = 1;
+    }
+
+    // 바이러스가 있는 위치 복사해서 사용
+    ArrayDeque<Node> queue = new ArrayDeque<>();
+    for (Node node : virus) {
+      queue.addLast(node);
+    }
+
+    // 바이러스(2)가 있는 위치 기준으로 BFS로 탐색하면서 전염시킴
+    while (!queue.isEmpty()) {
+      Node now = queue.poll();
+      // 4방향 이동
+      for (int i = 0; i < 4; i++) {
+        int ny = now.r + dy[i];
+        int nx = now.c + dx[i];
+
+        // 맵의 경계를 넘으면 넘김
+        if (ny < 0 || nx < 0 || ny >= N || nx >= M) {continue;}
+
+        // 전염될 수 있는 곳이면, 감염시킴 (방문처리도 같이 함)
+        if (cMap[ny][nx] == 0) {
+          cMap[ny][nx] = 2;
+          queue.addLast(new Node(ny, nx));
+        }
+
+      }
+    }
+
+    // 남아있는 빈칸(안전영역) 개수 세기
+    int count = 0;
+    for (int i = 0; i < N; i++) {
+      for (int j = 0; j < M; j++) {
+        if (cMap[i][j] == 0) {
+          count++;
+        }
+      }
+    }
+
+    return count;
+  }
+
+}

src/jaehoon/_11주차/BOJ_1940_주몽.java

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+package jaehoon._11주차;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.Arrays;
+import java.util.StringTokenizer;
+
+// https://www.acmicpc.net/problem/1940
+public class BOJ_1940_주몽 {
+
+  public static void main(String[] args) throws IOException {
+    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    int N = Integer.parseInt(br.readLine());
+    int M = Integer.parseInt(br.readLine());
+    StringTokenizer st = new StringTokenizer(br.readLine());
+    int[] arr = new int[N];
+    for (int i = 0; i < N; i++) {
+      arr[i] = Integer.parseInt(st.nextToken());
+    }
+    Arrays.sort(arr);
+
+    int count = 0;
+    int lt = 0, rt = N - 1;
+    while (lt < rt) {
+      int sum = arr[lt] + arr[rt];
+      if (sum == M) {
+        count++;
+        lt++;
+        rt--;
+        continue;
+      }
+      if (sum < M) {
+        lt++;
+      } else {
+        rt--;
+      }
+    }
+    System.out.println(count);
+    br.close();
+  }
+}