Cound Occurance in Sorted Array

package main

import (
    "fmt"
    "math"
    "sort"
)

func main() {
    res := countOcc([]int{10, 20, 20, 20, 40, 40, 50}, 20) // 3
    fmt.Println(res)
}

func countOcc(arr []int, target int) int {
    low := 0
    high := len(arr) - 1
    firstO := firstOcc(arr, low, high, target)
    if firstO == -1 {
        return 0
    }
    lastO := lastOcc(arr, low, high, target)
    return (lastO - firstO) + 1
}

func firstOcc(arr []int, low, high, target int) int {
    if low > high {
        return -1
    }
    mid := (low + high) / 2
    if arr[mid] < target {
        return firstOcc(arr, mid+1, high, target)
    } else if arr[mid] > target {
        return firstOcc(arr, low, mid-1, target)
    } else {
        if mid == 0 || arr[mid] != arr[mid-1] {
            return mid
        }
        return firstOcc(arr, low, mid-1, target)
    }
}

func lastOcc(arr []int, low, high, target int) int {
    if low > high {
        return -1
    }
    mid := (low + high) / 2
    if arr[mid] < target {
        return lastOcc(arr, mid+1, high, target)
    } else if arr[mid] > target {
        return lastOcc(arr, low, mid-1, target)
    } else {
        if mid == len(arr)-1 || arr[mid] != arr[mid+1] {
            return mid
        }
        return lastOcc(arr, low+1, high, target)
    }
}