package main
import (
"fmt"
"math"
)
func binarySearch(arr []int, val int) int {
var first = 0
var last = len(arr) - 1
for first <= last {
var midpoint = int(math.Floor(float64((first + last) / 2)))
if arr[midpoint] == val {
return midpoint
}
if val < arr[midpoint] {
last = midpoint - 1
} else {
first = midpoint + 1
}
}
return -1
}
func main() {
arr := []int{1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39}
fmt.Println(binarySearch(arr, 35))
}