LargestNumber.go

package main

import "fmt"

func main() {

	lg, positions := largestNumber([]int{71, 114, 105, 109, 84, 104, 101, 82, 101, 97, 112, 101, 114})

	fmt.Printf("Largest Number: %v\n", lg)
	fmt.Print("Positions: ")
	for _, v := range positions {
		fmt.Printf("%v ", v)
	}
	fmt.Println()

}

func largestNumber(na []int) (lg int, positions []int) {
	for i, v := range na {
		if v == lg {
			positions = append(positions, i)
		}
		if v > lg {
			lg = v
			positions = []int{i}
		}
	}
	return
}

Play with it: http://play.golang.org/p/0khLpSMOVU