[20250627] BOJ / P4 / 2048 (Hard) / 이강현

Author: lkhyun

lkhyun/202506/27 BOJ P4 2048 (Hard).md

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+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static int N;
+    static int ans = 0;
+
+    public static void main(String[] args) throws IOException {
+        N = Integer.parseInt(br.readLine());
+        int[][] board = new int[N][N];
+
+        for (int i = 0; i < N; i++) {
+            st = new StringTokenizer(br.readLine());
+            for (int j = 0; j < N; j++) {
+                board[i][j] = Integer.parseInt(st.nextToken());
+            }
+        }
+
+        backtracking(0, board);
+
+        bw.write(ans +"");
+        bw.close();
+    }
+    static void backtracking(int moveCnt, int[][] board) throws IOException {
+        if(moveCnt == 10) {
+            for (int i = 0; i < N; i++) {
+                for (int j = 0; j < N; j++) {
+                    ans = Math.max(ans, board[i][j]);
+                }
+            }
+            return;
+        }
+        int max = 0;
+        for (int i = 0; i < N; i++) {
+            for (int j = 0; j < N; j++) {
+                max = Math.max(max, board[i][j]);
+            }
+        }
+        if(max * (1<<(10 - moveCnt)) <= ans) return;
+        for (int k = 1; k <= 4; k++) {
+            int[][] newBoard = new int[N][N];
+            for (int i = 0; i < N; i++) {
+                System.arraycopy(board[i], 0, newBoard[i], 0, N);
+            }
+            move(k, newBoard);
+            backtracking(moveCnt + 1, newBoard);
+        }
+    }
+    static void move(int opt, int[][] board){ //1이면 위, 2면 아래, 3이면 왼쪽, 4면 오른쪽
+        boolean[][] visited = new boolean[N][N];
+        if(opt == 1) {
+            for (int i = 1; i < N; i++) {
+                for (int j = 0; j < N; j++) {
+                    if(board[i][j] == 0) { //빈칸이면 넘어감
+                        continue;
+                    }
+                    int tmp = i-1; //tmp는 현재 칸과 마주할 칸을 나타냄
+                    while(tmp >= 0 && board[tmp][j]==0){ //바로 윗칸이 빈칸이 아닐때까지 이동
+                        tmp--;
+                    }
+                    if(tmp<0){// 현재 칸 위가 다 빈칸일 경우
+                        board[0][j] = board[i][j]; //맨 윗칸에 현재칸 두고 끝
+                        board[i][j] = 0;
+                        continue;
+                    }
+                    if(board[i][j] == board[tmp][j] && !visited[tmp][j]){ //충돌시 같고 이미 합쳐진 블록이 아닐경우
+                        board[tmp][j] *= 2;
+                        visited[tmp][j] = true;
+                        board[i][j] = 0;
+                    }else{ //다르다면 tmp 한칸 앞에 그냥 둠
+                        board[tmp+1][j] = board[i][j];
+                        if(tmp+1 != i){ //tmp가 애초에 i랑 딱 붙어있을 경우에는 그대로가 유지되게 함.
+                            board[i][j] = 0;
+                        }
+                    }
+                }
+            }
+        }else if(opt == 2) {
+            for (int i = N-2; i >= 0; i--) {
+                for (int j = 0; j < N; j++) {
+                    if(board[i][j] == 0) {
+                        continue;
+                    }
+                    int tmp = i+1;
+                    while(tmp < N && board[tmp][j]==0){
+                        tmp++;
+                    }
+                    if(tmp>=N){
+                        board[N-1][j] = board[i][j];
+                        board[i][j] = 0;
+                        continue;
+                    }
+                    if(board[i][j] == board[tmp][j] && !visited[tmp][j]){
+                        board[tmp][j] *= 2;
+                        visited[tmp][j] = true;
+                        board[i][j] = 0;
+                    }else{
+                        board[tmp-1][j] = board[i][j];
+                        if(tmp-1 != i){
+                            board[i][j] = 0;
+                        }
+                    }
+                }
+            }
+        }else if(opt == 3) {
+            for (int j = 1; j < N; j++) {
+                for (int i = 0; i < N; i++) {
+                    if(board[i][j] == 0) {
+                        continue;
+                    }
+                    int tmp = j-1;
+                    while(tmp >= 0 && board[i][tmp]==0){
+                        tmp--;
+                    }
+                    if(tmp<0){
+                        board[i][0] = board[i][j];
+                        board[i][j] = 0;
+                        continue;
+                    }
+                    if(board[i][j] == board[i][tmp] && !visited[i][tmp]){
+                        board[i][tmp] *= 2;
+                        visited[i][tmp] = true;
+                        board[i][j] = 0;
+                    }else{
+                        board[i][tmp+1] = board[i][j];
+                        if(tmp+1 != j){
+                            board[i][j] = 0;
+                        }
+                    }
+                }
+            }
+        }else if(opt == 4) {
+            for (int j = N-2; j >= 0; j--) {
+                for (int i = 0; i < N; i++) {
+                    if(board[i][j] == 0) {
+                        continue;
+                    }
+                    int tmp = j+1;
+                    while(tmp < N && board[i][tmp]==0){
+                        tmp++;
+                    }
+                    if(tmp>=N){
+                        board[i][N-1] = board[i][j];
+                        board[i][j] = 0;
+                        continue;
+                    }
+                    if(board[i][j] == board[i][tmp] && !visited[i][tmp]){
+                        board[i][tmp] *= 2;
+                        visited[i][tmp] = true;
+                        board[i][j] = 0;
+                    }else{
+                        board[i][tmp-1] = board[i][j];
+                        if(tmp-1 != j){
+                            board[i][j] = 0;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+```