How does golang closure implement recursion

Golang closure is a very powerful language feature that allows us to define a function inside the function, and the function can access variables in the external function scope. The use of closures can greatly simplify code logic, making the code easier to read and maintain. In this article, we will introduce how to use Golang closures to implement recursion.

1. Recursion

Recursion is a process of the operating system stack. Its core idea is that a function can call itself during execution. Recursive functions can solve many complex problems, such as calculating Fibonacci numbers, binary tree traversal, and so on.

2. Simple recursive implementation

In Golang, two issues need to be paid attention to when implementing recursion:

1. There needs to be a termination condition, otherwise an infinite loop will occur. The problem.
2. Each recursion needs to pass data to the next recursion.

The following is a simple recursive implementation of calculating the factorial of n:

func factorial(n int) int {
    if n == 1 {
        return 1
    }
    return n * factorial(n-1)
}

3. Closure recursion

In Golang closure, we can A function is defined internally and the function can access variables in the scope of the outer function. Therefore, we can implement recursion through closures.

Taking the Fibonacci sequence as an example, the following is a simple program implemented using closure recursion:

func fibonacci() func() int {
    a, b := 0, 1
    return func() int {
        a, b = b, a+b
        return a
    }
}

func main() {
    f := fibonacci()
    for i := 0; i < 10; i++ {
        fmt.Println(f())
    }
}

This program will output the first ten terms of the Fibonacci sequence.

Code explanation:

First we define a function fibonacci, which returns a function. This function defines two variables a and b internally, which are used to represent the first two terms of the Fibonacci sequence.

Next, we return a function. This function uses closures internally to implement recursion. Each time the function is called, the values ​​of a and b are updated to the last b and a b, and the value of a is returned.

Finally, we call this function in the main function and print out the first ten values ​​of the Fibonacci sequence.

4. Application of closure recursion

Using closure recursion, we can implement many interesting applications, such as FizzBuzz problem, Towers of Hanoi, etc. The following takes Towers of Hanoi as an example to introduce how to use closure recursion.

Towers of Hanoi is a very classic mathematical problem. It is a divide-and-conquer algorithm implemented through recursion. The description of the problem is as follows:

There are three pillars, namely A, B and C. There are 64 discs of different sizes on pillar A. The discs of different sizes are placed on A in order from small to large. On the pillar, now all the discs need to be moved to pillar C. The following rules need to be followed during the movement:

1. Only one disc can be moved at a time.
2. The big disk cannot be on top of the small disk.

The following is the code that uses closure recursion to implement Towers of Hanoi:

func Hanoi(n int) func(string, string, string) {
    if n == 1 {
        return func(a, _, c string) {
            fmt.Println("Move disk from", a, "to", c)
        }
    }
    h := Hanoi(n - 1)
    return func(a, b, c string) {
        h(a, c, b)
        fmt.Println("Move disk from", a, "to", c)
        Hanoi(n-1)(b, a, c)
    }
}

func main() {
    Hanoi(3)("A", "B", "C")
}

This program will output the specific steps to move three disks from A to C.

Code explanation:

First we define a function Hanoi, which returns a function. If the passed-in parameter n is equal to 1, then a closure function is directly returned, which is responsible for moving the disk from pillar A to pillar C.

If the incoming n value is greater than 1, then first call Hanoi(n-1) recursively, then output the specific steps to move the disk from one pillar to another, and finally call Hanoi( n-1) Move the disk to pillar C.

Finally, we call this function in the main function and print out the specific moving steps.

5. Summary

In this article, we introduced the basic concepts and usage of Golang closures, and demonstrated the use of closures to recursively implement different problems through examples. Closure recursion is a very interesting and powerful programming technique, which can greatly simplify code logic and improve code readability and maintainability. Of course, closure recursion also needs to be used with caution, otherwise it may cause some unexpected problems.

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