Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
Scala Assignment: Recursion
package recfun
import scala.collection.mutable.ListBuffer
import common._
/** https://class.coursera.org/progfun-2012-001/assignment/view?assignment_id=4 */
object Main {
def main(args: Array[String]) {
println("Pascal's Triangle")
for (row <- 0 to 10) {
for (col <- 0 to row)
print(pascal(col, row) + " ")
println()
}
}
/**
* Exercise 1: Pascal's Triangle
*/
def pascal(c: Int, r: Int): Int = {
if (c == 0 || c == r) 1
else pascal(c - 1, r - 1) + pascal(c, r - 1)
}
/**
* Exercise 2: Parentheses Balancing
*/
def balance(chars: List[Char]): Boolean = {
def f(chars: List[Char], numOpens: Int): Boolean = {
if (chars.isEmpty) {
numOpens == 0
} else {
val h = chars.head
val n =
if (h == '(') numOpens + 1
else if (h == ')') numOpens - 1
else numOpens
if (n >= 0) f(chars.tail, n)
else false
}
}
f(chars, 0)
}
/**
* Exercise 3: Counting Change
* Write a recursive function that counts how many different ways you can make
* change for an amount, given a list of coin denominations. For example,
* there are 3 ways to give change for 4 if you have coins with denomiation
* 1 and 2: 1+1+1+1, 1+1+2, 2+2.
*/
def countChange(money: Int, coins: List[Int]): Int = {
def f(lastMaxCoin_total_coll: List[(Int, Int)], count: Int): Int = {
if (lastMaxCoin_total_coll.isEmpty) {
count
} else {
val b = ListBuffer[(Int, Int)]()
var newCount = count
for ((lastMaxCoin, total) <- lastMaxCoin_total_coll) {
if (total < money) {
for (c <- coins) {
if (c >= lastMaxCoin) {
val e = (c, total + c)
b += e
}
}
} else if (total == money) {
newCount += 1
}
}
f(b.toList, newCount)
}
}
val b = coins.map { c => (c, c) }
f(b, 0)
}
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment