这样写二分查找怎么不对呢
<br /><php <br />function binarySearch($arr,$a){<br /> <br /> $low = 0;<br /> $high = count($arr)-1;<br /> $mid = ceil(($low+$high)/2);<br /><br />while($low<=$high){<br /><br /> if($a==$arr[$mid]){<br /> echo "查找的数的位置是第"."$mid";<br /> }<br /><br /> if($a>$arr[$mid]){<br /><br /> $high = count($arr)-1;<br /> $low = $mid+1;<br /> $mid = ceil(($low+$high)/2);<br /> }<br /><br /> if ($a<$arr[$mid]) {<br /> <br /> $low = 0;<br /> $high = $mid-1;<br /> $mid = ceil(($low+$high)/2);<br /> }<br /> }<br />}<br />$arr1 = array(5,7,9,10,12,16,19);<br />binarySearch($arr1,12);<br /><br />?>登录后复制
------解决方案--------------------本帖最后由 xuzuning 于 2013-03-30 17:42:33 编辑 function binarySearch($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<=$high
&& $n++){
if($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<$arr[$mid]) {
$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){<br /> $low = 0;<br /> $high = count($arr)-1;<br /> $mid = ceil(($low+$high)/2);<br /> $num = count($arr);<br /> while($low<=$high && $num--){<br /> if($a==$arr[$mid]){<br /> echo "查找的数的位置是第"."$mid";<br /> break;<br /> }<br /> list($low, $high) = $a > $arr[$mid] ? array($mid, $high) : array($low, $mid);<br /> $mid = ceil(($low+$high)/2);<br /> }<br />}<br />登录后复制
------解决方案--------------------
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