Count One's

We need to count number 1's in given array. This array contains only 0's and 1's. The array is sorted means 1's are followed by 0's.

Input: arr[] = {0, 0, 1, 1, 1}
Output: 3

Input: arr[] = {1, 1, 1, 1}
Output: 4

Input: arr[] = {0, 0, 0}
Output: 0

Input: arr[] = {}
Output: 0

package main

import (
    "fmt"
)

func main() {
    nums := []int{0, 0, 1, 1, 1} // 3
    // target := 2
    count := countOnes(nums)
    fmt.Println(count)
}

func countOnes(nums []int) int {
    low := 0
    high := len(nums) - 1

    for low <= high {
        mid := (low + high) / 2
        if nums[mid] == 0 {
            low = mid + 1
        } else {
            if mid == 0 || nums[mid-1] == 0 {
                return len(nums) - mid
            }
            low = mid
        }
    }
    return 0
}