A Tour of Go - Exercise: Equivalent Binary Trees

A Tour of Go

Exercise: Equivalent Binary Trees

There can be many different binary trees with the same sequence of values stored at the leaves. For example, here are two binary trees storing the sequence 1, 1, 2, 3, 5, 8, 13.


A function to check whether two binary trees store the same sequence is quite complex in most languages. We'll use Go's concurrency and channels to write a simple solution.
This example uses the 

tree

 package, which defines the type:

type Tree struct {
Left  *Tree
Value int
Right *Tree
}

1. Implement the 

Walk

 function.

2. Test the 

Walk

 function.

The function 

tree.New(k)

 constructs a randomly-structured binary tree holding the values 

k

, 

2k

, 

3k

,
..., 

10k

.

Create a new channel 

ch

 and kick off the walker:

go Walk(tree.New(1), ch)

Then read and print 10 values from the channel. It should be the numbers 1, 2, 3, ..., 10.

3. Implement the 

Same

 function using 

Walk

 to determine whether 

t1

 and 

t2

store
the same values.

4. Test the 

Same

 function.

Same(tree.New(1), tree.New(1))

 should return true, and 

Same(tree.New(1), tree.New(2))

 should return false.

package main

import "tour/tree"
import "fmt"

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
if t.Left != nil {
Walk(t.Left, ch)
}
ch <- t.Value
if t.Right != nil {
Walk(t.Right, ch)
}
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
ch1 := make(chan int)
ch2 := make(chan int)

go Walk(t1, ch1)
go Walk(t2, ch2)

result := true
for i := 0; i < 10; i ++ {
v1 := <- ch1
v2 := <- ch2
result = (v1 == v2)
}

return result

}

func main() {
//	ch := make(chan int)
//	go Walk(tree.New(1), ch)
//	for i := 0; i < 10; i ++ {
//		v := <- ch
//		fmt.Println(v)
//	}

fmt.Println(Same(tree.New(1), tree.New(1)))
fmt.Println(Same(tree.New(1), tree.New(2)))

}