Swift. For loop iteration. - swift

Question

Using the following:
func isosceles(triangleSides: Int)
{
var y = 0
for _ in 1...triangleSides {
y = y + 1
var stringBuilder = String()
for _ in 1...y
{
stringBuilder += "*"
}
println(stringBuilder)
}
}
isosceles(3)
I can make the following pattern:
*
**
***
I'm trying to write a function that outputs a sideways triangle of height 2n-1 and width n, so the output for n = 4 would be:
*
**
***
**
*
func triangle(triangleSides: Int)
{
var y = 0
var x = 0
var index: Int
for _ in 1...triangleSides {
y = y + 1
var stringBuilder = String()
for _ in 1...y
{
stringBuilder += "*"
}
println(stringBuilder + "\n")
}
for _ in 1..<triangleSides{
x = triangleSides - 1
var index: Int
var stringBuilder = String()
for index in stride(from: triangleSides - 1, through: 1, by: -1) {
stringBuilder += "*"
}
println(stringBuilder + "\n")
}
}
I get
*
**
***
**
**
Obviously it's going to be me thats the problem with the way I am trying to do this. If somebody could point me in the right direction that would be appreciated.
Thanks

Answer 1

Well, there are quite a few things you're doing that you don't really need to do... but, your main problem is that your 3rd and 4th for loops are wrong.
The way it is now, it's looping from 1 to triangleSides - 1 in the outer loop and triangleSize - 1 to 1 in the inner loop. Since you're not using the actual index of the for loop, that just makes both the outer and inner loops run triangleSides - 1 times.
What you want to do is loop from triangleSize - 1 to 1 in your outer loop and 1 to the current value of your outer loop in your inner loop. It'll make it easier if you let the for loop do its job and assign x directly instead of ignoring the loop's index with _ and manually calculating x.
Those changes would look like this (just the second set of for loops):
for x in stride(from: triangleSides - 1, through: 1, by: -1) {
var stringBuilder = String()
for _ in 1...x {
stringBuilder += "*"
}
println(stringBuilder + "\n")
}
If you want to clean it up a little more, you can also let the for loop do its job in the first set of loops and get rid of the declarations of x, y, and index at the start of your function:
func triangle(triangleSides: Int)
{
for y in 1...triangleSides {
var stringBuilder = String()
for _ in 1...y
{
stringBuilder += "*"
}
println(stringBuilder + "\n")
}
for x in stride(from: triangleSides - 1, through: 1, by: -1) {
var stringBuilder = String()
for _ in 1...x {
stringBuilder += "*"
}
println(stringBuilder + "\n")
}
}
Now, this:
triangle(3)
Outputs:
*
**
***
**
*

Answer 2

Here is my version:
func triangle(triangleSides: Int)
{
var y = 0
var x = 0
var index: Int
var stringBuilder = ""
for _ in 1...triangleSides {
stringBuilder += "*"
println(stringBuilder)
}
for z in reverse(1..<triangleSides) {
let index = advance(stringBuilder.endIndex, -1)
stringBuilder = stringBuilder.substringToIndex(index)
println(stringBuilder)
}
}
triangle(4)
Output:
*
**
***
****
***
**
*
Comments. I think the double loop was too complex.