Find The Correct Possition of Given Missing number

• Find the correct index of given missing number
• Return -1 if it is already present

Input: arr[]={2, 4, 7, 9}, k= 5
Output: 2

Input: arr[]={2, 4, 7, 9}, k= 8
Output: 3

Input: arr[]={2, 4, 7, 9}, k= 4
Output: -1

package main

import (
    "fmt"
    "sort"
)

func main() {
    arr := []int{2, 4, 5, 7, 8}
    k := 6
    res := findMissingKsPositive(arr, k)
    fmt.Println(res)
}

func findMissingKsPositive(arr []int, k int) int {
    low := 0
    high := len(arr) - 1
    for low <= high {
        mid := (low + high) / 2
        if arr[mid] == k {
            return -1
        } else if arr[mid] < k {
            low = mid + 1
        } else if arr[mid] > k {
            high = mid - 1
        }
    }
    return low
}