Merge pull request #936 from AlgorithmWithGod/lkhyun

[20250920] BOJ / G4 / 롤러코스터 / 이강현

Author: ShinHeeEul

lkhyun/202509/20 BOJ G4 롤러코스터.md

@@ -0,0 +1,52 @@
+```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[] tops;
+    static int[] decrease;
+    static int[] increase;
+    
+    public static void main(String[] args) throws IOException {
+        N = Integer.parseInt(br.readLine());
+        tops = new int[N];
+        decrease = new int[N];
+        increase = new int[N];
+
+        st = new StringTokenizer(br.readLine());
+        for (int i = 0; i < N; i++) {
+            tops[i] = Integer.parseInt(st.nextToken());
+        }
+
+        for (int i = 0; i < N; i++) {
+            decrease[i] = 1;
+            for (int j = 0; j < i; j++) {
+                if (tops[j] > tops[i] && decrease[i] < decrease[j] + 1) {
+                    decrease[i] = decrease[j] + 1;
+                }
+            }
+        }
+
+        for (int i = N - 1; i >= 0; i--) {
+            increase[i] = 1;
+            for (int j = i + 1; j < N; j++) {
+                if (tops[i] < tops[j] && increase[i] < increase[j] + 1) {
+                    increase[i] = increase[j] + 1;
+                }
+            }
+        }
+
+        int maxLen = 0;
+        for (int i = 0; i < N; i++) {
+            maxLen = Math.max(maxLen, decrease[i] + increase[i] - 1);
+        }
+
+        bw.write(maxLen + "");
+        bw.close();
+    }
+}
+```