Introduction

Performance:
Binary Search Algorithm is a very commonly used searching algorithm. Because it’s very efficient in searching. It always works on the sorted array.

Source code:

function binarySearchJavaScript(array, keyElement)
{
    var lowerBound  = 0,
        upperBound   = array.length - 1,
        midValue = Math.floor((upperBound + lowerBound)/2);

    while(array[midValue] != keyElement && lowerBound < upperBound)
    {
       if (keyElement < array[midValue]) { upperBound = midValue - 1; } else if (keyElement > array[midValue])
        {
            lowerBound = midValue + 1;
        }

        midValue = Math.floor((upperBound + lowerBound)/2);
    }

    return (array[midValue] != keyElement) ? "Key element "+keyElement+" not found " : "Key element "+ keyElement +" found at position "+ midValue;
}

var array = [1, 2, 3, 4, 5, 7, 8, 9];
array.sort();
console.log(binarySearchJavaScript(array, 1));   
console.log(binarySearchJavaScript(array, 5));
console.log(binarySearchJavaScript(array, 10));
// output
// Key element 1 found at position 0
// Key element 5 found at position 4
// Key element 10 not found

function binarySearchPHP($array, $keyElement) 
{ 
    if (count($array) === 0) return false; 
    $lowerBound = 0; 
    $upperBound = count($array)-1; 
      
    while ($lowerBound <= $upperBound) { 
          
        $middleValue = floor(($lowerBound + $upperBound) / 2); 
   
        if($array[$middleValue] === $keyElement) { 
            return "$keyElement found at position ".$array[$middleValue]."\n"; 
        } 
  
        if ($keyElement &lt; $array[$middleValue]) { 
            $upperBound = $middleValue -1; 
        } 
        else { 
            $lowerBound = $middleValue + 1; 
        } 
    } 
      
    return "$keyElement not found...\n"; 
} 
  
$array = array(1, 2, 3, 4, 5,6,7,8,9,10); 
echo binarySearchPHP($array,2); 
echo binarySearchPHP($array,5); 
echo binarySearchPHP($array,11); 

// output
// 2 found at position 2
// 5 found at position 5
// 11 not found...

def binarySearchPython(item_list,item):
    lowerBound = 0
    upperBound = len(item_list)-1
    isFound = False
    while( lowerBound<=upperBound and not isFound):
        midValue = (lowerBound + upperBound)//2
        if item_list[midValue] == item :
            isFound = True
        else:
            if item &lt; item_list[midValue]:
                upperBound = midValue - 1
            else:
                lowerBound = midValue + 1    
    return isFound
    
print(binarySearchPython([1,2,3,5,8], 6))
print(binarySearchPython([1,2,3,5,8], 5))

 

Also, read What is Linear search?