/**
 * Demos of simple problems solved using recursion.
 * @author Sean Barker
 */
public class RecursionDemo {
    
    // iterative (not recursive!) implementation of factorial
    public static int factIter(int n) {
        int result = 1;
        for (int i = 1; i <= n; i++) {
            result = result * i;
        }
        return result;
    }
    
    // recursive implementation of factorial
    public static int fact2(int n) {
        if (n == 0) {
            // base case
            return 1;
        } else {
            // recursive case
            return n * fact2(n - 1);
        }
    }
    
    // sums values from 0 to n
    public static int sum(int n) {
        if (n == 0) {
            return 0;
        } else {
            return n + sum(n - 1);
        }
    }
    
    // compute base raised to power
    public static int exp(int base, int power) {
        if (power == 0) {
            return 1;
        } else {
            return base * exp(base, power - 1);
        }
    }
    
    // compute the nth fibonacci number (starting from 0)
    public static int fib(int n) {
        if (n <= 1) {
            return 1;
        } else {
            return fib(n - 1) + fib(n - 2);
        }
        
    }
    
    // return the length of s (without calling length)
    public static int strlen(String s) {
        if (s.equals("")) {
            return 0;
        } else {
            return strlen(s.substring(1)) + 1;
        }
    }
    
    // return a reversed version of s
    // allowed string methods: equals, substring, charAt
    public static String reverse(String s) {
        if (s.equals("")) {
            return "";
        } else {
            String subproblem = reverse(s.substring(1));
            return subproblem + s.charAt(0);
        }
    }

    // return s with all instances of c removed
    public static String removeChar(String s, char c) {
      if (s.equals("")) {
        return "";
      } else {
        String subcall = removeChar(s.substring(1), c);
        if (s.charAt(0) == c) {
          return subcall;
        } else {
          return s.charAt(0) + subcall;
        }
      }
    }
    
}