查找

1.顺序查找

$arr = array(1,2,3,4,4);
//顺序查找
function search($value, &$arr)
{
    $arr_search = array();
    foreach ($arr as $k=>$v)
    {
        if($v==$value)
        {
            $arr_search[$k] = $v;
        }
    }
    
    if(empty($arr_search))
    {
        return false;
    }else{
        return $arr_search;
    } 
}

var_dump(search(4,$arr));

 2.二分法查找

/**
 * 二分查找，前提是该数组必须是个有序的才行，如果不是必须先排序
 */
$arr = array(1,2,3,4,5,6);
function binarySearch($value, &$arr, $leftIndex, $rightIndex)
{
    if($rightIndex<$leftIndex)
    {
        echo '找不到该数';
        exit();
    }
    
    //首先找到中间数，并不一定非得是正中间
    $middleIndex = round(($rightIndex+$leftIndex)/2);
    
    //如果大于则，向后找
    if($value>$arr[$middleIndex]){
        binarySearch($value, $arr, $middleIndex+1, $rightIndex);
    }elseif($value<$arr[$middleIndex]){
        binarySearch($value, $arr, $leftIndex, $middleIndex-1);
    }else{
        echo '找到了，下标是：'.$middleIndex;
    }
}

print_r(binarySearch(6, $arr, 0, count($arr)-1));