go实例之排序

1、默认排序

　　使用sort包进行排序。排序是就地排序，因此它会更改给定的切片，并且不返回新的切片。

package main

import "fmt"
import "sort"

func main() {

    // Sort methods are specific to the builtin type;
    // here's an example for strings. Note that sorting is
    // in-place, so it changes the given slice and doesn't
    // return a new one.
    strs := []string{"c", "a", "b"}
    sort.Strings(strs)
    fmt.Println("Strings:", strs)

    // An example of sorting `int`s.
    ints := []int{7, 2, 4}
    sort.Ints(ints)
    fmt.Println("Ints:   ", ints)

    // We can also use `sort` to check if a slice is
    // already in sorted order.
    s := sort.IntsAreSorted(ints)
    fmt.Println("Sorted: ", s)
}

　　执行上面代码，将得到以下输出结果

Strings: [a b c]
Ints:    [2 4 7]
Sorted:  true

　　从上述代码可知，排序不同类型切片，调用不同接口，排序时直接对参数进行修改，排序接口不对排序后切片进行返回。

2、自定义排序

　　自定义排序需要我们声明一个相应类型，并实现sort.Interface-Len，Less，Swap在这个类型上，Less接口是正真的排序方法，Swap用于交换两个值，Len用于求出切片大小。如下示例代码，首先将原始 fruits 切片转换为ByLength来实现自定义排序，然后对该类型切片使用sort.Sort()方法。

图1 sort.Interface定义

　　其实自定义排序就是对接口的使用。针对ByLength结构重写了sort.Interface接口的方法。如图1所示，是在LiteIDE中sort.Interface的提示

package main

import "sort"
import "fmt"

// In order to sort by a custom function in Go, we need a
// corresponding type. Here we've created a `ByLength`
// type that is just an alias for the builtin `[]string`
// type.
type ByLength []string

// We implement `sort.Interface` - `Len`, `Less`, and
// `Swap` - on our type so we can use the `sort` package's
// generic `Sort` function. `Len` and `Swap`
// will usually be similar across types and `Less` will
// hold the actual custom sorting logic. In our case we
// want to sort in order of increasing string length, so
// we use `len(s[i])` and `len(s[j])` here.
func (s ByLength) Len() int {
    return len(s)
}
func (s ByLength) Swap(i, j int) {
    s[i], s[j] = s[j], s[i]
}
func (s ByLength) Less(i, j int) bool {
    return len(s[i]) < len(s[j])
}

// With all of this in place, we can now implement our
// custom sort by casting the original `fruits` slice to
// `ByLength`, and then use `sort.Sort` on that typed
// slice.
func main() {
    fruits := []string{"peach", "banana", "kiwi"}
    sort.Sort(ByLength(fruits))
    fmt.Println(fruits)
}

　　执行上面代码，将得到以下输出结果

[kiwi peach banana]