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 />
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------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 />
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------解决方案--------------------
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