We want to count all to the books in the library.You count up shelf #1,I count up shelf #2.
That's a map. The more people we get, the faster it gose.
我们要数图书馆里所有的书。你数1号书架的，我数2号书架的。这就是”map“。我们人数越多，就数的越快。
Now we get together and add our individual counts. that's reduce.
现在我们到一起，把所有人的统计数加在一起。这就是“Reduce”。