map中由于它内部有序，由红黑树保证，因此很多函数执行的时间复杂度都是log2N的，如果用map函数可以实现的功能，而STL Algorithm也可以完成该功能，建议用map自带函数，效率高一些。

-map due to its internal and orderly to ensure the tree by the red and black, many functions of the time complexity of the implementation are log2N, if map function can be achieved with the function of the STL Algorithm can also complete the features, it is recommended to use its own map function, higher efficiency.