let numbers = [1,3,4,5,9,1]
要找到前5个,请使用：
numbers.indexOf(5)
我如何找到第二次出现？
您可以在剩余的数组切片上执行另一个元素索引搜索,如下所示：
编辑/更新：Xcode 9•Swift 4
extension Collection where Element: Equatable {
func secondindex(of element: Element) -> Index? {
guard let index = index(of: element) else { return nil }
return self[self.index(after: index)...].index(of: element)
}
func indexes(of element: Element) -> [Index] {
var indexes: [Index] = []
var position = self.startIndex
while let index = self[position...].index(of: element) {
indexes.append(index)
position = self.index(after: index)
}
return indexes
}
}
测试：
let numbers = [1,1] numbers.secondindex(of: 5) // 4 numbers.indexes(of: 5) // [3,4]