I had an interview today and the person asked me this question:
How do you find easily an item in a circularly sorted array
Since I didn't know the answer, I tried to find a solution. Here's what I have:
Thanks
<?php
function searchincircularsorterlist($a, $len, $num) {
$start=0;
$end=$len-1;
$mid = 0;
while($start<$end) {
$mid=$start+$end/2;
if ($num == $a[$mid]) {
return $num;
}
if($num<$a[$mid]) {
if($num<$a[$start] && $a[$start]<=$a[$start+1])
$start=$mid++;
else
$end=$mid--;
}
else {
if($num>$a[$end] && $a[$end-1]<=$a[end])
$end=$mid--;
else
$start=$mid++;
}
}
if ($start == $end && $num == $a[$start]) {
return $num;
}
return -1;
}
$array = array(7,8,9,0,1,2,3,4,5,6);
var_dump(searchincircularsorterlist($array,sizeof($array),4));
I am trying to work with a circularly sorted array but for some reason it does not work. What's wrong with my code?
1) learn priority of operations. You should have: $mid=($start+$end)/2; which you ended up dividing $end by 2 and then $start - the result. This is why you got an infinite loop.
ReplyDelete2) use: $start=$mid+1; and not $start=$mid++; that will help reducing the number of loops
<?php
function searchincircularsorterlist($a, $len, $num) {
$start=0;
$end=$len-1;
$mid = 0;
while($start<$end) {
$mid=($start+$end)/2;
if ($num == $a[$mid]) {
return $num;
}
if($num<$a[$mid]) {
if($num<$a[$start] && $a[$start]<=$a[$start+1])
$start=$mid+1;
else
$end=$mid-1;
}
else {
if($num>$a[$end] && $a[$end-1]<=$a[end])
$end=$mid-1;
else
$start=$mid+1;
}
}
if ($start == $end && $num == $a[$start]) {
return $num;
}
return -1;
}
$array = array(7,8,9,0,1,2,3,4,5,6);
var_dump(searchincircularsorterlist($array,sizeof($array),4));