Created
June 1, 2015 03:32
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BinarySearch
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| <?php | |
| /* | |
| * Parameters: | |
| * $a - The sort array. | |
| * $first - First index of the array to be searched (inclusive). | |
| * $last - Last index of the array to be searched (exclusive). | |
| * $key - The key to be searched for. | |
| * $compare - A user defined function for comparison. Same definition as the one in usort | |
| * | |
| * Return: | |
| * index of the search key if found, otherwise return (-insert_index - 1). | |
| * insert_index is the index of smallest element that is greater than $key or sizeof($a) if $key | |
| * is larger than all elements in the array. | |
| */ | |
| function binary_search(array $a, $first, $last, $key, $compare) { | |
| $lo = $first; | |
| $hi = $last - 1; | |
| while ($lo <= $hi) { | |
| $mid = (int)(($hi - $lo) / 2) + $lo; | |
| $cmp = call_user_func($compare, $a[$mid], $key); | |
| if ($cmp < 0) { | |
| $lo = $mid + 1; | |
| } elseif ($cmp > 0) { | |
| $hi = $mid - 1; | |
| } else { | |
| return $mid; | |
| } | |
| } | |
| return -($lo + 1); | |
| } | |
| function cmp($a, $b) { | |
| return ($a < $b) ? -1 : (($a > $b) ? 1 : 0); | |
| } | |
| $a = array(1,2,3,4,5,6); | |
| $idx = binary_search($a, 0, sizeof($a), 4, 'cmp'); |
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