using combination to get a subset of a set of numbers and then calculate whether the sum of the subset equals a specific target

sum_subset.go

package main

import (
	"fmt"
	"math/big"
	"os"
)

var target int = 23813
var totalNum int = 69
var data []int = []int{396, 365, 238, 392, 378, 357, 402, 384, 348, 398, 370, 380, 396, 388, 341, 322, 370, 311, 396, 356, 380, 374, 327, 396, 388, 338, 331, 388, 356, 388, 381, 371, 374, 398, 372, 384, 286, 384, 391, 396, 400, 364, 372, 382, 378, 368, 398, 396, 379, 388, 438, 466, 380, 307, 378, 398, 388, 396, 394, 380, 378, 370, 388, 400, 324, 368, 378, 354, 406}

func fac(b int) *big.Int {
	r := big.NewInt(1)
	for i := 1; i < b; i++ {
		adder := big.NewInt(int64(i))
		r = r.Mul(r, adder)
	}
	return r
}

func combinationNum(n, m int) *big.Int {
	r1 := fac(n)
	r2 := fac(m)
	r3 := fac(n - m)
	r := r1.Div(r1, r2)
	r = r.Div(r, r3)
	return r
}

func printAry(a []int) {
	sum := sumInts(a)
	if sum == target {
		fmt.Println("found the target")

		for i := 0; i < len(a); i++ {
			fmt.Print(i)
			fmt.Print(",")
		}
		fmt.Println()
		for i := 0; i < len(a); i++ {
			fmt.Print(a[i])
			fmt.Print(",")
		}
		fmt.Println()

		for i := 0; i < len(a); i++ {
			fmt.Print(data[a[i]])
			fmt.Print(",")
		}
		fmt.Println()

		os.Exit(0)
	}
}

func combination(n, r int, proc func([]int)) {
	var ary []int = make([]int, r)
	var i, k int
	for i = 0; i < r; i++ {
		ary[i] = i
	}

	proc(ary)

	finished := false
	for !finished {
		finished = true
		for i = r - 1; i >= 0; i-- {
			if ary[i] < i+n-r {
				ary[i]++
				finished = false
				for k = i + 1; k < r; k++ {
					ary[k] = ary[k-1] + 1
				}
				proc(ary)
				break
			}
		}
	}
}

func sumInts(d []int) int {
	s := 0
	for i := 0; i < len(d); i++ {
		s += data[d[i]]
	}
	return s
}

func main() {

	for i := 68; i >= 57; i-- {

		stepNum := combinationNum(totalNum, i)

		fmt.Println("working on", i, "this step has", stepNum, "steps")

		combination(totalNum, i, printAry)
	}

}