[英]Swift equivalent of Ruby's “each_cons”
Ruby有each_cons可以像這樣使用
class Pair
def initialize(left, right)
@left = left
@right = right
end
end
votes = ["a", "b", "c", "d"]
pairs = votes.each_cons(2).map { |vote| Pair.new(*vote) }
p pairs
# [#<Pair @left="a", @right="b">, #<Pair @left="b", @right="c">, #<Pair @left="c", @right="d">]
swift中的代碼相同,但沒有each_cons
函數
struct Pair {
let left: String
let right: String
}
let votes = ["a", "b", "c", "d"]
var pairs = [Pair]()
for i in 1..<votes.count {
let left = votes[i-1]
let right = votes[i]
pairs.append(Pair(left: left, right: right))
}
print(pairs)
// [Pair(left: "a", right: "b"), Pair(left: "b", right: "c"), Pair(left: "c", right: "d")]
如何將這些快速代碼縮短或簡化?
zip(votes, votes.dropFirst())
這會產生一系列元組。
struct Pair {
let left: String
let right: String
}
let votes = ["a", "b", "c", "d"]
let pairs = zip(votes, votes.dropFirst()).map {
Pair(left: $0, right: $1)
}
print(pairs)
// [Pair(left: "a", right: "b"), Pair(left: "b", right: "c"), Pair(left: "c", right: "d")]
這是我提出的一般解決方案,但它看起來有點非常低效。 為了實現each_cons(n)
我的設置clump
來n
:
let arr = [1,2,3,4,5,6,7,8]
let clump = 2
let cons : [[Int]] = arr.reduce([[Int]]()) {
memo, cur in
var memo = memo
if memo.count == 0 {
return [[cur]]
}
if memo.count < arr.count - clump + 1 {
memo.append([])
}
return memo.map {
if $0.count == clump {
return $0
}
var arr = $0
arr.append(cur)
return arr
}
}
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