Lecture 19

Question 1

One classic application for recursion is for use in

Answer 1

sorting

Question 2

Merge Sort

Answer 2

merge two pre-sorted arrays.
–If we have two presorted arrays, then the smallest overall element must be in the first slot of one of the two arrays.
–It dramatically reduces the effort needed to find each element in its proper order.

Question 3

Binary tree code

Answer 3

template 
class TreeNode
{
public:
K key;
V value;
TreeNode* left;
TreeNode* right;
}

Question 4

Binary tree print

Answer 4

void print(TreeNode* node)
{
if(node == 0) return;
print(node.left);
cout << node.value << “ ”;
print(node.right);
}

Question 5

Code for using recursion with factorials, but stopping at a certain number.

Answer 5

int factorial(int i, int n)
{
if(i >= n)
return n;
else return i * factorial(i+1, n);
}

Question 6

factorial helper method

Answer 6

int factorialStarter(int n)
{
if(n < 0) throw exception();
else if(n==0) return 1;
else return factorial(1, n);
}

Question 7

what is a helper method

Answer 7

It’s so named because its sole reason to
exist is to help setup the needed
parameters and such for the true,
underlying method.

Question 8

A tail-recursive method is one in which

Answer 8

all of the computation is done during the initial method calls.

Question 9

factorial tail recursion

Answer 9

int factorial(int part, int n)
{
if(n == 0 || n == 1)
return part;
else
return factorial(part * n, n-1);
}