PHP算法-二分法查找 博客分类： PHP PHP算法二分法

**
 * 二分法查找
 * 在有序数组中查询
 *
 * @param int $needle            
 * @param array $arr            
 */
function dichotomize_search($needle, $arr)
{
    $count = count($arr);
    if ($count < 1) {
        return false;
    }
    if ($count == 1) {
        if ($count == $needle) {
            return 0;
        } else {
            return false;
        }
    }
    $first = 0;
    $last = $count - 1;
    
    while ($first <= $last) {
        $mid = floor(($first + $last) / 2);
        if ($arr[$mid] > $needle) {
            $last = $mid - 1;
        } else 
            if ($arr[$mid] < $needle) {
                $first = $mid - 1;
            } else {
                return $mid;
            }
    }
    return false;
}