[20250920] BOJ / G4 / 체스판 다시 칠하기 2 / 김민진

Author: zinnnn37

zinnnn37/202509/20 BOJ G4 체스판 다시 칠하기 2.md

@@ -0,0 +1,79 @@
+```java
+package etc;
+
+import java.io.*;
+import java.util.StringTokenizer;
+
+public class BJ_25682_체스판_다시_칠하기_2 {
+
+	private static final boolean BLACK = true;
+	private static final boolean WHITE = false;
+
+	private static final BufferedReader  br = new BufferedReader(new InputStreamReader(System.in));
+	private static final BufferedWriter  bw = new BufferedWriter(new OutputStreamWriter(System.out));
+	private static       StringTokenizer st;
+
+	private static int N, M, K;
+
+	private static boolean[][] board;
+	private static int[][]     prefix;
+
+	public static void main(String[] args) throws IOException {
+		init();
+		sol();
+	}
+
+	private static void init() throws IOException {
+		st = new StringTokenizer(br.readLine());
+		N  = Integer.parseInt(st.nextToken());
+		M  = Integer.parseInt(st.nextToken());
+		K  = Integer.parseInt(st.nextToken());
+
+		board  = new boolean[N + 1][M + 1];
+		prefix = new int[N + 1][M + 1];
+
+		for (int i = 1; i <= N; i++) {
+			String s = br.readLine();
+			for (int j = 1; j <= M; j++) {
+				board[i][j] = s.charAt(j - 1) == 'B' ? BLACK : WHITE;
+			}
+		}
+	}
+
+	private static void sol() throws IOException {
+		bw.write(Math.min(setPrefix(BLACK), setPrefix(WHITE)) + "\n");
+		bw.flush();
+		bw.close();
+		br.close();
+	}
+
+	// 열 + 행이 짝수일 때 color라고 가정
+	private static int setPrefix(boolean color) {
+		int val;
+
+		for (int i = 1; i <= N; i++) {
+			for (int j = 1; j <= M; j++) {
+				if ((i + j) % 2 == 0) {
+					val = board[i][j] != color ? 1 : 0;
+				} else {
+					val = board[i][j] == color ? 1 : 0;
+				}
+				prefix[i][j] = prefix[i][j - 1] + prefix[i - 1][j] - prefix[i - 1][j - 1] + val;
+			}
+		}
+		return getMinPrefix();
+	}
+
+	private static int getMinPrefix() {
+		int cnt = Integer.MAX_VALUE;
+
+		for (int i = K; i <= N; i++) {
+			for (int j = K; j <= M; j++) {
+				cnt = Math.min(cnt, prefix[i][j] - prefix[i - K][j] - prefix[i][j - K] + prefix[i - K][j - K]);
+			}
+		}
+		return cnt;
+	}
+
+}
+```