refactor(p2190B1): simplify MainPlus logic and replace BufferedReader

Author: lzwjava

src/main/java/com/lzw/solutions/codeforces/p2190B1/MainPlus.java

@@ -1,46 +1,58 @@
-// gpt
 package com.lzw.solutions.codeforces.p2190B1;
 
-import java.io.BufferedReader;
-import java.io.InputStreamReader;
+import java.util.*;
 
 public class MainPlus {
-    public static void main(String[] args) throws Exception {
-        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
-        StringBuilder out = new StringBuilder();
-
-        int t = Integer.parseInt(br.readLine().trim());
-        while (t-- > 0) {
-            int n = Integer.parseInt(br.readLine().trim());
-            String s = br.readLine().trim();
-
-            // Precompute suffix counts of '(' and ')'
-            int[] sufOpen = new int[n + 1];
-            int[] sufClose = new int[n + 1];
-
-            for (int i = n - 1; i >= 0; i--) {
-                sufOpen[i] = sufOpen[i + 1];
-                sufClose[i] = sufClose[i + 1];
-                if (s.charAt(i) == '(') sufOpen[i]++;
-                else sufClose[i]++;
-            }
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        int t = sc.nextInt();
+
+        for (int test = 0; test < t; test++) {
+            int n = sc.nextInt();
+            String s = sc.next();
 
-            int answer = -1;
+            int ans = -1;
 
-            // Try to skip the earliest ')' that allows a valid suffix RBS
+            // Try every possible first difference position i (0-based)
+            // where we change s[i] from ) to (
             for (int i = 0; i < n; i++) {
-                if (s.charAt(i) == ')') {
-                    int pairs = Math.min(sufOpen[i + 1], sufClose[i + 1]);
-                    if (pairs > 0) {
-                        answer = 2 * pairs;
+                if (s.charAt(i) != ')') continue;
+
+                // simulate prefix up to i (with s[i] changed to '(' )
+                int bal = 0;
+                boolean valid = true;
+                for (int j = 0; j < i; j++) {
+                    bal += (s.charAt(j) == '(' ? 1 : -1);
+                    if (bal < 0) {
+                        valid = false;
                         break;
                     }
                 }
+                if (!valid) continue;
+
+                // now add the changed '('
+                bal += 1;
+                if (bal < 0) continue;  // though unlikely here
+
+                // now from i+1 to end, greedily take as far as possible
+                // while keeping bal >= 0, and stop when bal returns to 0
+                int len = i + 1;           // 0-based: positions 0..i
+                int startBal = bal;
+
+                for (int j = i + 1; j < n; j++) {
+                    bal += (s.charAt(j) == '(' ? 1 : -1);
+                    if (bal < 0) break;
+                    len++;
+                    if (bal == 0) {
+                        // found a valid completion
+                        ans = Math.max(ans, len);
+                        break;  // no need to go further — longer won't be prefix-equal
+                    }
+                }
             }
 
-            out.append(answer).append('\n');
+            System.out.println(ans);
         }
-
-        System.out.print(out.toString());
+        sc.close();
     }
-}
+}