第1章　算法简介 code

 'use strict'; function binary_search(list, item) { let low = 0; let high = list.length - 1;  while (low <= high) { let mid = Math.floor((low + high) / 2); let guess = list[mid]; if (guess === item) { return mid;    } if (guess > item) {      high = mid - 1;    } else {      low = mid + 1;    }  }  return null;} const my_list = [1, 3, 5, 7, 9]; console.log(binary_search(my_list, 3)); // 1console.log(binary_search(my_list, -1)); // null 
 <?phpfunction binarySearch($needle, $array) { $low = 0; $high = count($array) - 1; while ($low <= $high) { $middle = floor(($low + $high) / 2); if ($array[$middle] == $needle) { return $middle;    } if ($array[$middle] > $needle) { $high = $middle - 1;    } else { $low = $middle + 1;    }  } return null;}$array = [1, 3, 5, 7, 9];echo binarySearch(3, $array) . "\n";echo binarySearch(-1, $array) . "\n";