binary search

main.go

package main

import "fmt"

func BinarySearch(array []int, element int) int {
	low := 0
	high := len(array) - 1

	for low <= high {
		index := (high + low) / 2

		if element == array[index] {
			return index
		}

		if element < array[index] {
			high = index - 1
		} else {
			low = index + 1
		}
	}
	return -1
}

func ResultMessage(got int, expected int) {
	if got != expected {
		fmt.Printf("Incorrect, got: %d, expected: %d.\n", got, expected)
	} else {
		fmt.Printf("Correct, got: %d, expected: %d.\n", got, expected)
	}
}

func TestBinarySearch(array []int, element int, expected int) {
	got := BinarySearch(array, element)
	ResultMessage(got, expected)
}

func main() {
	TestBinarySearch([]int{1, 2, 3}, 2, 1)
	TestBinarySearch([]int{1, 2, 3, 4}, 2, 1)
	TestBinarySearch([]int{1, 2, 3, 4, 5}, 2, 1)
	TestBinarySearch([]int{1, 2, 3, 4, 5}, 4, 3)
}

main.rb

def binary_search(array, element)
  low, high = 0, array.size - 1

  while low <= high
    index = (high + low)/2

    return index if element == array[index]

    if element < array[index]
      high = index - 1
    else
      low = index + 1
    end
  end

  return -1
end

puts binary_search([1,2,3], 2)
puts binary_search([1,2,3,4], 2)
puts binary_search([1,2,3,4,5], 2)
puts binary_search([1,2,3,4,5], 4)
puts binary_search([1,2,3,4,5], 0)

def find_second_element(array, element)
  index = binary_search(array, element)
  return -1 if index == -1

  if array[index - 1] == element
    while array[index - 1] == element
      index = index - 1
    end
    return index + 1
  end
  return index + 1 if array[index + 1] == element
  return -1
end
puts find_second_element([1,2,2,2,5], 0)
puts find_second_element([1,2,5], 2)
puts find_second_element([1,2,2,5], 2)
puts find_second_element([1,2,2,2,2,2,5], 2)
puts find_second_element([1,1,1,1,2,2,5], 2)
puts find_second_element([1,1,1,1,2,2,2,2,5], 2)