EXC_I386_GPFLT in Swift code using Xcode Playground - swift

Question

I ran the same code in Xcode 7beta/rc Playground project and got an error:
Execution was interrupted, reason: EXC_BAD_ACCESS(code=EXC_I386_GPFLT)
in
let n: Int = Int(Process.arguments[1])!
How do I solve in Playground project since other solutions don't seem to be related?
Binary tree: http://benchmarksgame.alioth.debian.org/u64q/program.php?test=binarytrees&lang=swift&id=1
class TreeNode {
var left, right : TreeNode?
var item : Int
init(_ left: TreeNode?, _ right: TreeNode?, _ item: Int) {
self.left = left
self.right = right
self.item = item
}
func check() -> Int {
guard let left = left, let right = right else {
return item
}
return item + left.check() - right.check()
}
}
func bottomUpTree(item: Int, _ depth: Int) -> TreeNode {
if depth > 0 {
return
TreeNode(
bottomUpTree(2*item-1, depth-1),
bottomUpTree(2*item, depth-1),
item
)
}
else {
return
TreeNode(nil,nil,item)
}
}
let n: Int = Int(Process.arguments[1])!
let minDepth = 4
let maxDepth = n
let stretchDepth = n + 1
let check = bottomUpTree(0,stretchDepth).check()
print("stretch tree of depth \(stretchDepth)\t check: \(check)")
let longLivedTree = bottomUpTree(0,maxDepth)
var depth = minDepth
while depth <= maxDepth {
let iterations = 1 << (maxDepth - depth + minDepth)
var check = 0
for i in 0..<iterations {
check += bottomUpTree(i,depth).check()
check += bottomUpTree(-i,depth).check()
}
print("\(iterations*2)\t trees of depth \(depth)\t check: \(check)")
depth += 2
}
print("long lived tree of depth \(maxDepth)\t check: \(longLivedTree.check())")

Answer 1

Process.arguments holds the value that is passed as arguments for a command-line application.
But you're using it in a Playground: there's no access to command line input from a Playground (they are Sandboxed), so Process.arguments is nil and your app crashes when you're doing Process.arguments[1].
The solution is to use this in an actual application, not in a Playground.

Answer 2

You can use a custom "readLine()" function and a global input variable, each element in the input array is presenting a line:
import Foundation
var currentLine = 0
let input = ["5", "5 6 3"]
func readLine() -> String? {
if currentLine < input.endIndex {
let line = input[currentLine]
currentLine += 1
return line
} else {
return nil
}
}
let firstLine = readLine() // 5
let secondLine = readLine() // 5 6 3
let thirdLine = readLine() // nil