Recursion on Strings

Part of: Recursion

Strings Are Recursive Too. A String can be viewed as a first character plus the rest of the string. That self-similar structure makes strings perfect for recursion. The key tools are: - s.length(), number of characters; length() == 0 is the natural base case. - s.substring(0, 1), the first character as a one-character string. - s.substring(1), everything except the first character (the smaller problem). Reversing a String. To reverse, put the first character last : reverse the rest, then append the first character. Trace reverse("cat"): - reverse("cat") = reverse("at") + 'c' - reverse("at") = reverse("t") + 'a' - reverse("t") = "t" (base case) - Build up: "t" + "a" = "ta", then "ta" + "c" = "tac" Counting Occurrences. The same pattern counts a target character: check the first char, then recurse on the rest. Why This Pattern Works. Each call handles one character and delegates the remaining n-1 characters to a recursive call. Because the string shrinks by one each time, it always reaches the empty (or single-char) base case. What usually goes wrong. What you see What caused it How to fix it --- --- --- The word comes back unchanged The first character was rejoined on the side it st

Challenge: Recursive String Reverse