Swift:第二次出现 indexOf [英] Swift: second occurrence with indexOf
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问题描述
let numbers = [1,3,4,5,5,9,0,1]
要找到第一个 5
,请使用:
To find the first 5
, use:
numbers.indexOf(5)
如何找到第二次出现?
推荐答案
- 列表项
您可以在剩余的数组切片上再次搜索元素的索引,如下所示:
You can perform another search for the index of element at the remaining array slice as follow:
编辑/更新:Swift 5.2 或更高版本
extension Collection where Element: Equatable {
/// Returns the second index where the specified value appears in the collection.
func secondIndex(of element: Element) -> Index? {
guard let index = firstIndex(of: element) else { return nil }
return self[self.index(after: index)...].firstIndex(of: element)
}
}
extension Collection {
/// Returns the second index in which an element of the collection satisfies the given predicate.
func secondIndex(where predicate: (Element) throws -> Bool) rethrows -> Index? {
guard let index = try firstIndex(where: predicate) else { return nil }
return try self[self.index(after: index)...].firstIndex(where: predicate)
}
}
测试:
let numbers = [1,3,4,5,5,9,0,1]
if let index = numbers.secondIndex(of: 5) {
print(index) // "4
"
} else {
print("not found")
}
if let index = numbers.secondIndex(where: { $0.isMultiple(of: 3) }) {
print(index) // "5
"
} else {
print("not found")
}
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