// 1. 统计每个元素出现次数
The deal was announced by the Federal Trade Commission (FTC) and a group of 11 states, of leaving the drivers on its Spark Driver app tens of millions of dollars out of pocket.
，更多细节参见旺商聊官方下载
items in it. append can just place the item in the existing backing
There's also Stream.broadcast() for push-based multi-consumer scenarios. Both require you to think about what happens when consumers run at different speeds — because that's a real concern that shouldn't be hidden.