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// Go's concurrency primitives make it easy to
// express concurrent concepts, such as
// this binary tree comparison.
//
// Trees may be of different shapes,
// but have the same contents. For example:
//
// 4 6
// 2 6 4 7
// 1 3 5 7 2 5
// 1 3
//
// This program compares a pair of trees by
// walking each in its own goroutine,
// sending their contents through a channel
// to a third goroutine that compares them.
package main
import (
"fmt"
"math/rand"
)
// A Tree is a binary tree with integer values.
type Tree struct {
Left *Tree
Value int
Right *Tree
}
// Walk traverses a tree depth-first,
// sending each Value on a channel.
func Walk(t *Tree, ch chan int) {
if t == nil {
return
}
Walk(t.Left, ch)
ch <- t.Value
Walk(t.Right, ch)
}
// Walker launches Walk in a new goroutine,
// and returns a read-only channel of values.
func Walker(t *Tree) <-chan int {
ch := make(chan int)
go func() {
Walk(t, ch)
close(ch)
}()
return ch
}
// Compare reads values from two Walkers
// that run simultaneously, and returns true
// if t1 and t2 have the same contents.
func Compare(t1, t2 *Tree) bool {
c1, c2 := Walker(t1), Walker(t2)
for {
v1, ok1 := <-c1
v2, ok2 := <-c2
if !ok1 || !ok2 {
return ok1 == ok2
}
if v1 != v2 {
break
}
}
return false
}
// New returns a new, random binary tree
// holding the values 1k, 2k, ..., nk.
func New(n, k int) *Tree {
var t *Tree
for _, v := range rand.Perm(n) {
t = insert(t, (1+v)*k)
}
return t
}
func insert(t *Tree, v int) *Tree {
if t == nil {
return &Tree{nil, v, nil}
}
if v < t.Value {
t.Left = insert(t.Left, v)
return t
}
t.Right = insert(t.Right, v)
return t
}
func main() {
t1 := New(100, 1)
fmt.Println(Compare(t1, New(100, 1)), "Same Contents")
fmt.Println(Compare(t1, New(99, 1)), "Differing Sizes")
fmt.Println(Compare(t1, New(100, 2)), "Differing Values")
fmt.Println(Compare(t1, New(101, 2)), "Dissimilar")
}
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