Write a function that takes
an array of characters and reverses the
letters in place.
Why an array of
characters instead of a string?
The goal of this
question is to practice manipulating arrays
in place. Since Swift strings support
unicode, a single character in a string might
be multiple bytes. There's
no way to get
the ith character in a
Swift string.
To sidestep this complexity, we'll work with
arrays of characters instead, which let us
quickly access characters at any offset.
In general, an in-place algorithm will require swapping elements.
We swap the first and last characters, then the second and second-to-last characters, and so on until we reach the middle.
func reverse(_ str: inout [Character]) {
guard str.count > 0 else {
return
}
var leftIndex = 0
var rightIndex = str.count - 1
while leftIndex < rightIndex {
// swap characters
let leftChar = str[leftIndex]
let rightChar = str[rightIndex]
str[leftIndex] = rightChar
str[rightIndex] = leftChar
// move towards middle
leftIndex += 1
rightIndex -= 1
}
}
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It's easy and quick. No "reset password" flow. No password to forget.
It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
It makes it harder for one person to share a paid Interview Cake account with multiple people.
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