binarySearch.js

/*-----------------------------------------------------------------------------		
the reference is from UdemyCourse: LearningAlgorithmsInJavascriptFromScratch		
-----------------------------------------------------------------------------*/		

function binarySearch(numArr, key) {
  numArr = numArr.sort((a, b) => a - b);

  var midIndex = Math.floor(numArr.length / 2);
  var midElement = numArr[midIndex];


  // if less than key, then after splicing, the array contains midElement
  // remember splice() need to be assigned to a new variable
  // splice(startIndex, HowMany)
  

  if (midElement === key) return true;
  // 留下後面，contain midElement
  else if (midElement < key && numArr.length > 1) {
    return binarySearch(numArr.splice(midIndex), key);
  } 
  // 留下前面
  else if (midElement > key && numArr.length > 1) {
    return binarySearch(numArr.splice(0, midIndex), key);
  } 
  else return false;
  
}

binarySearch([5, 7, 12, 16, 36, 39, 42, 56, 71], 15);