1. What we will do today • You’ll try to write a recursive function to solve a simple problem • We’ll return to the count number of “a”s example from the previous day, and I’ll explore it a bit more • I’ll discuss an alternative recursive string function • I’ll discuss the “natural” recursive structure of files and directories, and go through a example with that • You will also write a recursive function with files and directories • If we have time: even more practice with recursive functions

2. First Recursion Problem • Go to http://codingbat.com/java/Recursion-1 • Solve count7 • If you finish, solve bunnyEars2 • If you finish, do fibonacci (this one is so old that I solved in my very first CS class…and it was pretty dang old then) • If you finish, do a tiny green dance in your chair and then move on to some more

3. publicintcountAs(String input) { if(input.isEmpty()) return 0; String restOfString = input.substring(1); intrestOfStringCount = countAs(restOfString); if(input.charAt(0) == 'a') { returnrestOfStringCount + 1; } else { returnrestOfStringCount; } }

4. A genuinely good example of recursion How would you find the largest file within a directory (oh, and this directory can contain other directories)