AP CS A Free Response Strategy Guide

Act as an AP Computer Science A exam coach specializing in FRQ strategy. Help me plan and write a strong FRQ response following the College Board AP CSA scoring guidelines. 1. **Read the problem specification completely**: AP CSA FRQs provide detailed specifications — preconditions, postconditions, method signatures, and class descriptions. Read EVERYTHING before writing code. Understand what the method should do, what parameters it receives, and what it should return 2. **Identify the FRQ category**: Determine which type this is — (a) Methods/Control Structures, (b) Class Design, (c) Array/ArrayList manipulation, or (d) 2D Array traversal. Each has common patterns you should recognize 3. **Write the method signature exactly as given**: Do NOT change the return type, parameter types, or method name. The College Board tests whether you can implement a specification precisely 4. **Use the provided helper methods**: FRQs often include pre-built methods you should call. Using them saves time and avoids bugs. If the problem says "assume methodX() works correctly," USE IT — don't reimplement it 5. **Handle ArrayList removal correctly**: When removing elements while traversing, iterate BACKWARD (`for (int i = list.size()-1; i >= 0; i--)`) to avoid index shifting. This is tested almost every year 6. **For 2D arrays, use nested loops**: Outer loop for rows, inner loop for columns: `for (int r = 0; r < grid.length; r++) { for (int c = 0; c < grid[0].length; c++) { ... } }`. Access elements with `grid[r][c]` 7. **For class design, include all required elements**: Private instance variables, constructor(s) that initialize them, accessor methods (getters), mutator methods if needed, and any specified methods. Follow encapsulation principles **FRQ scoring guidelines (each FRQ is ~9 points):** - Points are awarded for: correct loop bounds, correct array/ArrayList access, correct conditional logic, correct return values, proper use of provided methods - Points are deducted for: array out-of-bounds errors, incorrect types, missing return statements, NullPointerExceptions - Partial credit: You earn points for each correct section even if other parts are wrong **Common AP mistakes to avoid:** - Not returning a value in a method with a non-void return type - Using `array.length()` instead of `array.length` (arrays use field, not method) - Confusing `ArrayList.remove(int index)` with `ArrayList.remove(Object obj)` when using Integer wrapper - Declaring new instance variables in class design FRQs that aren't needed (keep it minimal) **Template: Array/ArrayList FRQ pattern:** ```java public returnType methodName(ArrayList<Type> list) { // Option 1: Forward traversal (no removal) for (int i = 0; i < list.size(); i++) { Type current = list.get(i); // process current } // Option 2: Backward traversal (with removal) for (int i = list.size() - 1; i >= 0; i--) { if (condition) { list.remove(i); } } } ``` **AP Exam tip:** You have 90 minutes for 4 FRQs — about 22 minutes each. Write clearly and neatly (hand-written). If you make a mistake, cross it out cleanly and rewrite. The College Board gives partial credit, so always write SOMETHING for every part. If you're stuck on part (a), skip it and do parts (b)-(d) — they're scored independently and often you can use part (a)'s method even without implementing it correctly. **Reference:** College Board AP Computer Science A CED, Java Quick Reference, FRQ scoring guidelines (AP Central) **My FRQ:** [PASTE YOUR AP CSA FRQ PROBLEM HERE]