[백준 17829] 222-풀링 - 분할정복

Author: HiiWee

hoseok/week78/Boj17829.java

@@ -0,0 +1,115 @@
+// BOTTOM_UP
+import java.io.*;
+import java.util.*;
+
+class Main {
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+        int n = Integer.parseInt(br.readLine());
+        int[][] map = new int[n][n];
+
+        for (int i = 0; i < n; i++) {
+            StringTokenizer st = new StringTokenizer(br.readLine());
+            for (int j = 0; j < n; j++) {
+                map[i][j] = Integer.parseInt(st.nextToken());
+            }
+        }
+
+        while (n / 2 > 0) {
+            n = n / 2;
+            int[][] nextMap = new int[n][n];
+
+            for (int i = 0; i < n; i++) {
+                for (int j = 0; j < n; j++) {
+                    nextMap[i][j] = getSecondMaxNumber(i * 2, j * 2, map);
+                }
+            }
+            map = nextMap;
+        }
+
+        bw.write(Integer.toString(map[0][0]));
+        bw.flush();
+        bw.close();
+    }
+
+    public static int getSecondMaxNumber(int r, int c, int[][] map) {
+        int maxNumber = -10000;
+        int secondMaxNumber = -10000;
+        for (int i = r; i < r + 2; i++) {
+            for (int j = c; j < c + 2; j++) {
+                if (maxNumber < map[i][j]) {
+                    secondMaxNumber = maxNumber;
+                    maxNumber = map[i][j];
+                } else {
+                    secondMaxNumber = Math.max(secondMaxNumber, map[i][j]);
+                }
+            }
+        }
+        return secondMaxNumber;
+    }
+}
+
+// TOP_DOWN
+import java.io.*;
+import java.util.*;
+
+class Main {
+
+    static final int[] ROWS = {0, 1, 1, 0};
+    static final int[] COLS = {0, 0, 1, 1};
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+        int n = Integer.parseInt(br.readLine());
+        int[][] map = new int[n][n];
+
+        for (int i = 0; i < n; i++) {
+            StringTokenizer st = new StringTokenizer(br.readLine());
+            for (int j = 0; j < n; j++) {
+                map[i][j] = Integer.parseInt(st.nextToken());
+            }
+        }
+
+        bw.write(Integer.toString(polling(0, 0, n, map)));
+        bw.flush();
+        bw.close();
+    }
+
+    public static int polling(int r, int c, int n, int[][] map) {
+        int maxNumber = -10000;
+        int secondMaxNumber = -10000;
+        if (n == 2) {
+            for (int i = r; i < r + 2; i++) {
+                for (int j = c; j < c + 2; j++) {
+                    if (maxNumber < map[i][j]) {
+                        secondMaxNumber = maxNumber;
+                        maxNumber = map[i][j];
+                    } else {
+                        secondMaxNumber = Math.max(secondMaxNumber, map[i][j]);
+                    }
+                }
+            }
+
+            return secondMaxNumber;
+        }
+
+        int size = n / 2;
+        for (int i = 0; i < 4; i++) {
+            int nextR = r + size * ROWS[i];
+            int nextC = c + size * COLS[i];
+
+            int number = polling(nextR, nextC, size, map);
+
+            if (maxNumber < number) {
+                secondMaxNumber = maxNumber;
+                maxNumber = number;
+            } else {
+                secondMaxNumber = Math.max(secondMaxNumber, number);
+            }
+        }
+
+        return secondMaxNumber;
+    }
+}