拓扑排序(go,闭包,匿名函数)
// prereqs记录了每个课程的前置课程
var prereqs = map[string][]string{
"algorithms": {"data structures"},
"calculus": {"linear algebra"},
"compilers": {
"data structures",
"formal languages",
"computer organization",
},
"data structures": {"discrete math"},
"databases": {"data structures"},
"discrete math": {"intro to programming"},
"formal languages": {"discrete math"},
"networks": {"operating systems"},
"operating systems": {"data structures", "computer organization"},
"programming languages": {"data structures", "computer organization"},
}
unc main() {
for i, course := range topoSort(prereqs) {
fmt.Printf("%d:\t%s\n", i+1, course)
}
}
func topoSort(m map[string][]string) []string {
var order []string
seen := make(map[string]bool)
var visitAll func(items []string)
visitAll = func(items []string) {
for _, item := range items {
if !seen[item] {
seen[item] = true
visitAll(m[item])
order = append(order, item)
}
}
}
var keys []string
for key := range m {
keys = append(keys, key)
}
sort.Strings(keys)
visitAll(keys)
return order
}
当匿名函数需要被递归调用时,我们必须首先声明一个变量(在上面的例子中,我们首先声明了 visitAll),再将匿名函数赋值给这个变量。如果不分成两部,函数字面量无法与visitAll绑定,我们也无法递归调用该匿名函数。
visitAll := func(items []string) {
// ...
visitAll(m[item]) // compile error: undefined: visitAll
// ...
}
结果如下:
1: intro to programming
2: discrete math
3: data structures
4: algorithms
5: linear algebra
6: calculus
7: formal languages
8: computer organization
9: compilers
10: databases
11: operating systems
12: networks
13: programming languages
小结:
这个思想和java有出入,递归不一定要另外新建方法,可以使用提前声明+匿名函数 然后再函数内部调用进行递归