这样写二分查找如何不对呢

程序员文章站 2024-01-29 10:50:40

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这样写二分查找怎么不对呢



function binarySearch($arr,$a){


    $low = 0;

    $high = count($arr)-1;

    $mid = ceil(($low+$high)/2);


while($low


    if($a==$arr[$mid]){

    	echo "查找的数的位置是第"."$mid";

    }


    if($a>$arr[$mid]){


        $high = count($arr)-1;

    	$low = $mid+1;

	    $mid = ceil(($low+$high)/2);

    }


    if ($a
    	

    	$low = 0;

    	$high = $mid-1;

    	$mid = ceil(($low+$high)/2);

    }

  }

}

$arr1 = array(5,7,9,10,12,16,19);

binarySearch($arr1,12);


?>

------解决方案--------------------

本帖最后由 xuzuning 于 2013-03-30 17:42:33 编辑 function binarySearch($arr,$a){

$low = 0;
$high = count($arr)-1;
$mid = ceil(($low+$high)/2);
$n = 0;防止死循环的措施
while($low&& $n++){
if($a==$arr[$mid]){
echo "查找的数的位置是第"."$mid";
break;
}

if($a>$arr[$mid]){

$high = count($arr)-1;
$low = $mid-1;//注意这里
$mid = ceil(($low+$high)/2);
}

if ($a
$low = 0;
$high = $mid+1;//注意这里
$mid = ceil(($low+$high)/2);
}
}
}
------解决方案--------------------
按 php 实际可写作

function binarySearch($arr,$a){

  $low = 0;

  $high = count($arr)-1;

  $mid = ceil(($low+$high)/2);

  $num = count($arr);

  while($low
    if($a==$arr[$mid]){

      echo "查找的数的位置是第"."$mid";

      break;

    }

    list($low, $high) = $a > $arr[$mid] ? array($mid, $high) : array($low, $mid);

    $mid = ceil(($low+$high)/2);

  }

}

------解决方案--------------------