Я понял.
for i in 0..<5{
// 5,4,3,2,1 - " "
for _ in stride(from: 5, to: i, by: -1){
print(" ", terminator:"")
}
// 1,2,3,4,5 - "*"
for _ in stride(from: 0, through: i, by: 1){
print("*", terminator:"")
}
// 0,1,2,3,4 - "*"
for _ in stride(from: 1, through: i, by: 1){
print("*", terminator:"")
}
print(" ")
}