체스판위의 공

pr/체스판위의 공/Main.java

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+import java.io.*;
+import java.util.*;
+
+public class Main {
+    public static void main(String[] args) {
+        new Main().run();
+    }
+
+    public void run() {
+        FastReader fr = new FastReader();
+        if (!fr.hasMoreTokens())
+            return;
+        int n = fr.nextInt();
+        int m = fr.nextInt();
+        int[][] grid = new int[n][m];
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                grid[i][j] = fr.nextInt();
+            }
+        }
+
+        int[][] result = this.solve(n, m, grid);
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                sb.append(result[i][j]).append(" ");
+            }
+            sb.append("\n");
+        }
+        System.out.print(sb.toString());
+    }
+
+    public int n, m;
+    public int[][] grid;
+
+    // x, y 좌표를 각각 따로 메모하면 메모리도 아끼고 처리도 빠릅니다.
+    public int[][] memoX;
+    public int[][] memoY;
+
+    public int[][] solve(int n, int m, int[][] grid) {
+        this.n = n;
+        this.m = m;
+        this.grid = grid; // 필드 변수 할당 필수!
+        int[][] result = new int[n][m];
+
+        memoX = new int[n][m];
+        memoY = new int[n][m];
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++)
+                memoX[i][j] = -1; // 초기화
+        }
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                int[] dest = findDest(i, j);
+                result[dest[0]][dest[1]]++;
+            }
+        }
+        return result;
+    }
+
+    public int[] findDest(int x, int y) {
+        // 1. 이미 아는 길이면 바로 리턴
+        if (memoX[x][y] != -1) {
+            return new int[] { memoX[x][y], memoY[x][y] };
+        }
+
+        int currX = x, currY = y;
+
+        // 2. 재귀 대신 while문으로 종착지까지 달리기 (StackOverflow 방지)
+        while (true) {
+            int minX = currX, minY = currY;
+            int minVal = grid[currX][currY];
+
+            for (int i = 0; i < 8; i++) {
+                int nx = currX + dx[i], ny = currY + dy[i];
+                if (nx < 0 || nx >= n || ny < 0 || ny >= m)
+                    continue;
+                if (grid[nx][ny] < minVal) {
+                    minVal = grid[nx][ny];
+                    minX = nx;
+                    minY = ny;
+                }
+            }
+
+            // 멈출 곳을 찾았다면?
+            if (minX == currX && minY == currY)
+                break;
+
+            // 만약 다음 칸의 종착지를 이미 안다면? 바로 거기라고 메모하고 끝내기
+            if (memoX[minX][minY] != -1) {
+                currX = memoX[minX][minY];
+                currY = memoY[minX][minY];
+                break;
+            }
+
+            currX = minX;
+            currY = minY;
+        }
+
+        // 3. 찾은 종착지를 메모지에 적어두기
+        memoX[x][y] = currX;
+        memoY[x][y] = currY;
+        return new int[] { currX, currY };
+    }
+
+    public int[] dx = { -1, -1, -1, 0, 0, 1, 1, 1 };
+    public int[] dy = { -1, 0, 1, -1, 1, -1, 0, 1 };
+
+    static class FastReader {
+        BufferedReader br;
+        StringTokenizer st;
+
+        public FastReader() {
+            br = new BufferedReader(new InputStreamReader(System.in));
+        }
+
+        public String next() {
+            while (st == null || !st.hasMoreElements()) {
+                try {
+                    st = new StringTokenizer(br.readLine());
+                } catch (IOException e) {
+                }
+            }
+            return st.nextToken();
+        }
+
+        public int nextInt() {
+            return Integer.parseInt(next());
+        }
+
+        public long nextLong() {
+            return Long.parseLong(next());
+        }
+
+        public boolean hasMoreTokens() {
+            while (st == null || !st.hasMoreElements()) {
+                String line = null;
+                try {
+                    line = br.readLine();
+                } catch (IOException e) {
+                }
+                if (line == null)
+                    return false;
+                st = new StringTokenizer(line);
+            }
+            return true;
+        }
+    }
+}