[20251206] BOJ / G4 / 우유 도시 / 이강현

lkhyun/202512/06 BOJ G4 우유 도시.md

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+```java
+import java.util.*;
+import java.io.*;
+
+public class Main{
+    static class State{
+        int lastMilk;
+        int cnt;
+        State(int lastMilk,int cnt){
+            this.lastMilk = lastMilk;
+            this.cnt = cnt;
+        }
+    }
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static StringBuilder sb = new StringBuilder();
+    static int N;
+    static int[][] stores;
+    static State[][] dp;
+
+    public static void main(String[] args) throws Exception {
+        N = Integer.parseInt(br.readLine());
+        stores = new int[N+1][N+1];
+
+        for(int i = 1; i<=N; i++){
+            st = new StringTokenizer(br.readLine());
+            for(int j = 1; j <= N; j++){
+                stores[i][j] = Integer.parseInt(st.nextToken());
+            }
+        }
+
+        dp = new State[N+1][N+1];
+
+        if(stores[1][1] == 0){
+            dp[1][1] = new State(0, 1);
+        }else{
+            dp[1][1] = new State(-1, 0);
+        }
+
+
+        for(int j = 2; j <= N; j++){
+            int nextMilk = (dp[1][j-1].lastMilk + 1) % 3;
+            if(dp[1][j-1].lastMilk == -1) nextMilk = 0;
+
+            if(stores[1][j] == nextMilk){
+                dp[1][j] = new State(stores[1][j], dp[1][j-1].cnt + 1);
+            }else{
+                dp[1][j] = new State(dp[1][j-1].lastMilk, dp[1][j-1].cnt);
+            }
+        }
+
+        for(int i = 2; i <= N; i++){
+            int nextMilk = (dp[i-1][1].lastMilk + 1) % 3;
+            if(dp[i-1][1].lastMilk == -1) nextMilk = 0;
+
+            if(stores[i][1] == nextMilk){
+                dp[i][1] = new State(stores[i][1], dp[i-1][1].cnt + 1);
+            }else{
+                dp[i][1] = new State(dp[i-1][1].lastMilk, dp[i-1][1].cnt);
+            }
+        }
+
+        for(int i = 2; i<=N;i++){
+            for(int j = 2; j<=N; j++){
+                State up = dp[i-1][j];
+                State left = dp[i][j-1];
+
+                int upNextMilk = (up.lastMilk + 1) % 3;
+                if(up.lastMilk == -1) upNextMilk = 0;
+
+                int leftNextMilk = (left.lastMilk + 1) % 3;
+                if(left.lastMilk == -1) leftNextMilk = 0;
+
+                int upCnt = up.cnt + (stores[i][j] == upNextMilk ? 1 : 0);
+                int leftCnt = left.cnt + (stores[i][j] == leftNextMilk ? 1 : 0);
+
+                if(upCnt >= leftCnt){
+                    if(stores[i][j] == upNextMilk){
+                        dp[i][j] = new State(stores[i][j], upCnt);
+                    }else{
+                        dp[i][j] = new State(up.lastMilk, upCnt);
+                    }
+                }else{
+                    if(stores[i][j] == leftNextMilk){
+                        dp[i][j] = new State(stores[i][j], leftCnt);
+                    }else{
+                        dp[i][j] = new State(left.lastMilk, leftCnt);
+                    }
+                }
+            }
+        }
+        bw.write(dp[N][N].cnt+"");
+        bw.close();
+    }
+}
+```