// A concurrent solution to finding Pythagorean triplets with sum 5000

package main

import "fmt"

// Representation of Pythagorean triplets
type Triplet [3]int

// Find Pythagorean triplets starting with values from channel 'in'.
// Send the triplets to channel 'out'.
func FindPythTriplets(in <-chan int, out chan<- Triplet, maxsum int) {
    i := <-in // Receive value from 'in'.
    for i < maxsum {
        for j := i+1; i+j < maxsum; j++ {
            for k := j+1; i+j+k <= maxsum; k++ {
       	        if i*i + j*j == k*k {
    		    out <- Triplet{i,j,k} // Send triplet to 'out'.
    		}
    	    }
        }
        i = <-in  // Get next start value
    }
}

// Send the sequence 1, 2, 3, 4, ... to channel 'ch'.
func Generate(ch chan<- int) {
	for i := 1; ; i++ {
		ch <- i // Send 'i' to channel 'ch'.
	}
}

// The main operation: create workers and receive results
func main() {
        const sum = 5000          // the sum we are searching
        const numworkers = 20     // number of workers

	numbers := make(chan int)      // create new channel with numbers
        go Generate(numbers)
	triplets := make(chan Triplet) // create new channel for results
        for i := 1; i <= numworkers; i++ { // create workers
            go FindPythTriplets(numbers, triplets, sum)
        }

        ts := Triplet{0,0,0}
	for ts[0]+ts[1]+ts[2] != sum {
	   ts = <- triplets
	}
        fmt.Println(ts)
}

/*
Execution:

    > time go run pythagorean.go

...with specifying used processors:

    > export GOMAXPROCS=1 && time go run pythagorean.go
    > export GOMAXPROCS=2 && time go run pythagorean.go
    > export GOMAXPROCS=4 && time go run pythagorean.go
    > export GOMAXPROCS=8 && time go run pythagorean.go

Run-time (Thinkpad T14s, i7-1165G7 @ 2.8GHz, 8 processors, in seconds)
with setting GOMAXPROCS=<n>
1:  2.95
2:  1.60
4:  0.89
8:  0.86
*/