ADD file via upload

src/BracketManager.java

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+import java.util.List;
+import java.util.Random;
+
+/**
+ * 负责生成并添加括号
+ */
+public class BracketManager {
+  private static final Random RANDOM = new Random();
+  
+  /**
+   * 根据元素个数选择括号对数
+   * 3 -> 80% 1对 20%0对
+   * 4 -> 90% 1对 10%2对
+   * 5 -> 50% 1对 50%2对
+   */
+  public int decideParenthesesPairs(int numCount) {
+    return switch (numCount) {
+      case 3 -> RANDOM.nextDouble() < 0.8 ? 1 : 0;
+      case 4 -> RANDOM.nextDouble() < 0.9 ? 1 : 2;
+      case 5 -> RANDOM.nextDouble() < 0.5 ? 1 : 2;
+      default -> 0;
+    };
+  }
+  
+  // 添加括号
+  public String addParentheses(String expression, int pairs, List<Integer> numPositions) {
+    String[] tokens = expression.split(" ");
+    int numCount = numPositions.size();
+    boolean[] markLeft = new boolean[numCount];
+    boolean[] markRight = new boolean[numCount];
+    
+    generateBracketPositions(numCount, numPositions, pairs, tokens, markLeft, markRight);
+    String result = insertBrackets(tokens, markLeft, markRight);
+    return validateParentheses(result) ? result : expression;
+  }
+  
+  //计算生成括号的位置
+  private void generateBracketPositions(int numCount, List<Integer> numPositions, int pairs, String[] tokens,
+                                        boolean[] markLeft, boolean[] markRight) {
+    int attempts = 0;
+    for (int p = 0; p < pairs && attempts < 50; p++, attempts++) {
+      boolean placed = false;
+      for (int tries = 0; tries < 50 && !placed; tries++) {
+        int start = RANDOM.nextInt(numCount - 1);
+        int end = start + 1 + RANDOM.nextInt(numCount - start - 1);
+        if (end >= numCount) end = numCount - 1;
+        
+        // 20%概率尝试嵌套在已有括号内部
+        if (RANDOM.nextDouble() < 0.2) {
+          for (int i = 0; i < numCount; i++) {
+            if (markLeft[i]) {
+              start = i;
+              end = i + RANDOM.nextInt(numCount - i);
+              break;
+            }
+          }
+        }
+        
+        if (canPlaceBracket(start, end, markLeft, markRight, numPositions, tokens)) {
+          markLeft[start] = true;
+          markRight[end] = true;
+          placed = true;
+        }
+      }
+    }
+  }
+  
+  //检测添加括号的合法性
+  private boolean canPlaceBracket(int start, int end, boolean[] markLeft, boolean[] markRight,
+                                  List<Integer> numPositions, String[] tokens) {
+    if (isOuterMostBracket(start, end, markLeft.length)) return false;
+    if (isInvalidOverlap(start, end, markLeft, markRight)) return false;
+    return isValidBracketRange(tokens, numPositions, start, end);
+  }
+  
+  //避免最外层括号
+  private boolean isOuterMostBracket(int start, int end, int numCount) {
+    return start == 0 && end == numCount - 1;
+  }
+  
+  //允许嵌套但禁止交叉
+  private boolean isInvalidOverlap(int start, int end, boolean[] markLeft, boolean[] markRight) {
+    for (int i = start; i <= end; i++) {
+      // start/end可重合，内部禁止已有左右括号
+      if ((i != start && markLeft[i]) || (i != end && markRight[i])) return true;
+    }
+    return false;
+  }
+  
+  //检测括号是否有意义（优先级）
+  private boolean isValidBracketRange(String[] tokens, List<Integer> numPositions, int start, int end) {
+    int opStart = numPositions.get(start) + 1;
+    int opEnd = numPositions.get(end) - 1;
+    String firstOp = null;
+    boolean hasHigherOuterOp = false;
+    
+    for (int i = opStart; i <= opEnd; i += 2) {
+      if (!isNumber(tokens[i])) {
+        if (firstOp == null) firstOp = tokens[i];
+        else if (isDifferentPriority(firstOp, tokens[i])) {
+          hasHigherOuterOp = true;
+          break;
+        }
+      }
+    }
+    return hasHigherOuterOp || firstOp == null;
+  }
+  
+  //比较运算符优先级
+  private boolean isDifferentPriority(String op1, String op2) {
+    int p1 = (op1.equals("+") || op1.equals("-")) ? 1 : 2;
+    int p2 = (op2.equals("+") || op2.equals("-")) ? 1 : 2;
+    return p1 != p2;
+  }
+  
+  //插入操作
+  private String insertBrackets(String[] tokens, boolean[] markLeft, boolean[] markRight) {
+    StringBuilder sb = new StringBuilder();
+    int numIndex = 0;
+    for (String token : tokens) {
+      if (isNumber(token)) {
+        if (markLeft[numIndex]) sb.append("( ");
+        sb.append(token);
+        if (markRight[numIndex]) sb.append(" )");
+        numIndex++;
+      } else {
+        sb.append(" ").append(token).append(" ");
+      }
+    }
+    return sb.toString();
+  }
+  
+  //检查括号是否缺失
+  private boolean validateParentheses(String expr) {
+    int balance = 0;
+    for (char c : expr.toCharArray()) {
+      if (c == '(') balance++;
+      if (c == ')') balance--;
+      if (balance < 0) return false;
+    }
+    return balance == 0;
+  }
+  
+  private boolean isNumber(String token) {
+    try { Integer.parseInt(token); return true; }
+    catch (NumberFormatException e) { return false; }
+  }
+}