i have some problem.
i just want my loop to run, but when i try to do it, it fails, it has to increment each letter by a few, but it doesn't take any new letters at all, why is this happening and what is the reason? in c ++ such code would work.
function accum('ZpglnRxqenU') {
// your code
$result = '';
$letters_result = '';
$letter_original = '';
$num_if_str = strlen($s);
$j = 0;
for ( $i=0; $i <= $num_if_str; $i++ )
{
$letter_original = substr($s, $i, $i+1);
$j = 0;
while($j == $i)
{
$letters_result = $letters_result . $letter_original;
$j++;
}
if($i != strlen($s))
{
$letters_result = $letters_result . '-';
}
}
return $letters_result;
}
It returns
- Expected: 'Z-Pp-Ggg-Llll-Nnnnn-Rrrrrr-Xxxxxxx-Qqqqqqqq-Eeeeeeeee-Nnnnnnnnnn-Uuuuuuuuuuu'
Actual : 'Z-----------'
what problem with what PHP code?
There are a number of problems here:
you're using $s but never initialise it
Your call to substr() uses an incorrect value for the length of substring to return
you're inner loop only runs while $i = $j, but you initialise $j to 0 so it will only run when $i is zero, i.e. for the first letter of the string.
There is a simpler way to do this. In PHP you can address individual characters in a string as if they were array elements, so no need for substr()
Further, you can use str_repeat() to generate the repeating strings, and if you store the expanded strings in an array you can join them all with implode().
Lastly, combining ucwords() and strtolower() returns the required case.
Putting it all together we get
<?php
$str = "ZpglnRxqenU";
$output = [];
for ($i = 0;$i<strlen($str);$i++) {
$output[] = str_repeat($str[$i], $i+1);
}
$output = ucwords(strtolower(implode('-',$output)),"-");
echo $output; // Z-Pp-Ggg-Llll-Nnnnn-Rrrrrr-Xxxxxxx-Qqqqqqqq-Eeeeeeeee-Nnnnnnnnnn-Uuuuuuuuuuu
Demo:https://3v4l.org/OoukZ
I don't have much more to add to #TangentiallyPerpendicular's answer as far as critique, other than you've made the classic while($i<=strlen($s)) off-by-one blunder. String bar will have a length of 3, but arrays are zero-indexed [eg: [ 0 => 'b', 1 => 'a', '2' => 'r' ]] so when you hit $i == strlen() at 3, that's an error.
Aside from that your approach, when corrected and made concise, would look like:
function accum($input) {
$result = '';
for ( $i=0, $len=strlen($input); $i < $len; $i++ ) {
$letter = substr($input, $i, 1);
for( $j=0; $j<=$i; $j++ ) {
$result .= $letter;
}
if($i != $len-1) {
$result .= '-';
}
}
return $result;
}
var_dump(accum('ZpglnRxqenU'));
Output:
string(76) "Z-pp-ggg-llll-nnnnn-RRRRRR-xxxxxxx-qqqqqqqq-eeeeeeeee-nnnnnnnnnn-UUUUUUUUUUU"
Also keep in mind that functions have their own isolated variable scope, so you don't need to namespace variables like $letters_foo which can make your code a bit confusing to the eye.
Some time ago during a job interview I got the task to reverse a string in PHP without using strrev.
My first solution was something like this:
$s = 'abcdefg';
$temp = '';
for ($i = 0, $length = mb_strlen($s); $i < $length; $i++) {
$temp .= $s{$length - $i - 1};
}
var_dump($temp);
// outputs string(7) "gfedcba"
then they asked me if I could do this without doubling the memory usage (not using the $temp variable or any variable to copy the reversed string to) and I failed.
This kept bugging me and since then I tried to solve this multiple times but I constantly failed.
My latest try looks like this:
$s = 'abcdefg';
for ($i = 0, $length = mb_strlen($s); $i < $length; $i++) {
$s = $s{$i * 2} . $s;
}
var_dump($s);
// outputs string(14) "gfedcbaabcdefg"
It's not a solution to chop off "abcdefg" after the loop because then I would still double the amount of memory used. I need to remove the last character in every iteration of the loop.
I tried to use mb_substr like this:
$s = 'abcdefg';
for ($i = 0, $length = mb_strlen($s); $i < $length; $i++) {
$s = $s{$i * 2} . mb_substr($s, $length - $i - 1, 1);
}
var_dump($s);
but it only gives me Uninitialized string offset errors.
This is where I'm stuck (again). I tried googling but all the solutions I found either echo the characters directly or use a temporary variable.
I also found the Question PHP String reversal without using extra memory but there's no answer that fits my needs.
That's an interesting one.
Here's something I just came up with:
$s = 'abcdefghijklm';
for($i=strlen($s)-1, $j=0; $j<$i; $i--, $j++) {
list($s[$j], $s[$i]) = array($s[$i], $s[$j]);
}
echo $s;
list() can be used to assign a list of variables in one operation. So what I am doing is simply swapping characters (starting with first and last, then second-first and second-last and so on, till it reaches the middle of the string)
Output is mlkjihgfedcba.
Not using any other variables than $s and the counters, so I hope that fits your criteria.
You can use the fact that in PHP a string can be thought of as an array of characters.
Then basically what you want to do is to replace each character $i on the left side of the middle of the string with the character $j on the right side of the middle with the same distance.
For example, in a string of seven characters the middle character is on position 3. The character on position 0 (distance 3) needs to be swapped with the character on position 6 (3 + 3), the character on position 1 (distance 2) needs to be swapped with the character on position 5 (3 + 2), etc.
This algorithm can be implemented as follows:
$s = 'abcdefg';
$length = strlen($s);
for ($i = 0, $j = $length-1; $i < ($length / 2); $i++, $j--) {
$t = $s[$i];
$s[$i] = $s[$j];
$s[$j] = $t;
}
var_dump($s);
$string = 'abc';
$reverted = implode(array_reverse(str_split($string)));
You could use the XOR swap trick.
function rev($str) {
$len = strlen($str);
for($i = 0; $i < floor($len / 2); ++$i) {
$str[$i] = $str[$i] ^ $str[$len - $i - 1];
$str[$len - $i - 1] = $str[$i] ^ $str[$len - $i - 1];
$str[$i] = $str[$i] ^ $str[$len - $i - 1];
}
return $str;
}
print rev("example");
Try this:
$s = 'abcdefg';
for ($i = strlen($s)-1; $i>=0; $i--) {
$s .= $s[$i];
$s[$i] = NULL;
}
var_dump(trim($s));
Here it is PHP7 version of this:
echo "\u{202E}abcdefg"; // outs: gfedcba
PHP strings are kinda-sorta mutable, but due to copy-on-write it's very difficult to modify them in-place without a copy being made. Some of the above solutions work, but only because they're stand-alone; some already fail because they define a function without a pass-by-reference argument. To get the code to actually operate in-place in a larger program, you'd need to pay careful attention to assignments, function arguments, and scopes.
Example:
$string1 = 'abc';
$string2 = $string1;
$string1[0] = 'b';
print("$string1, $string2");
> "abc, bbc"
I suppose that if between initializing the variable and modifying it you only ever used by-reference assignments (&=) and reference arguments (function rev(&$string)) (or assign the string to an object property initially, and then never assign it to any other variable), you might be able to change the original value of the string without making any copies. That's a bit ridiculous, however, and I'd assume that the interviewer who came up with that question didn't know about copy-on-write.
This isn't quite the same as immutability in other languages, by the way, because it applies to arrays too:
$a = [0, 1, 2];
$b = $a;
$b[0] = 1;
print(implode($a).implode($b));
> "012112"
To sum up, all types (except for objects as of PHP5) are assigned with copy-on-write unless you specifically use the &= operator. The assignment doesn't copy them, but unlike most other languages (C, Java, Python...) that either change the original value (arrays) or don't allow write access at all (strings), PHP will silently create a copy before making any changes.
Of course, if you switched to a language with more conventional pointers and also switched to byte arrays instead of strings, you could use XOR to swap each pair of characters in place:
for i = 0 ... string.length / 2:
string[i] ^= string[string.length-1-i]
string[string.length-1-i] ^= string[i]
string[i] ^= string[string.length-1-i]
Basically #EricBouwers answer, but you can remove the 2nd placeholder variable $j
function strrev2($str)
{
$len = strlen($str);
for($i=0;$i<$len/2;$i++)
{
$tmp = $str[$i];
$str[$i] = $str[$len-$i-1];
$str[$len-$i-1] = $tmp;
}
return $str;
}
Test for the output:
echo strrev2("Hi there!"); // "!ereht iH"
echo PHP_EOL;
echo strrev2("Hello World!"); // "!dlroW olleH"
This will go through the list and stop halfway, it swaps the leftmost and rightmost, and works it's way inward, and stops at the middle. If odd numbered, the pivot digit is never swapped with itself, and if even, it swaps the middle two and stops. The only extra memory used is $len for convenience and $tmp for swapping.
If you want a function that doesn't return a new copy of the string, but just edits the old one in place you can use the following:
function strrev3(&$str)
{
$len = strlen($str);
for($i=0;$i<$len/2;$i++)
{
$tmp = $str[$i];
$str[$i] = $str[$len-$i-1];
$str[$len-$i-1] = $tmp;
}
}
$x = "Test String";
echo $x; // "Test String"
strrev3($x);
echo PHP_EOL;
echo $x; // "gnirtS tseT"
Using &$str passes a direct pointer the the string for editing in place.
And for a simpler implementation like #treegardens, you can rewrite as:
$s = 'abcdefghijklm';
$len = strlen($s);
for($i=0; $i < $len/2; $i++) {
list($s[$i], $s[$len-$i-1]) = array($s[$len-$i-1], $s[$i]);
}
echo $s;
It has the similar logic, but I simplified the for-loop quite a bit.
Its Too Simple
//Reverse a String
$string = 'Basant Kumar';
$length = strlen($string);
for($i=$length-1;$i >=0;$i--){
echo $string[$i];
}
Here is my code to solve your problem
<?php
$s = 'abcdefg';
for ($i = 0, $length = mb_strlen($s); $i < $length; $i++) {
$s = $s{$i}.mb_substr($s,0,$i).mb_substr($s,$i+1);
}
var_dump($s);
?>
You could also use a recursion to reverse the string. Something like this for example:
function reverse($s) {
if(strlen($s) === 1) return $s;
return substr($s, strlen($s)-1) . reverse(substr($s , 0, strlen($s)-1));
}
What you do here is actually returning the last character of the string and then calling again the same function with the substring that contains the initial string without the last character. When you reach the point when your string is just one character then you end the recursion.
You can use this code to reverse a string without using the reserved function in php.
Code:
<?php
function str_rev($y)// function for reversing a string by passing parameters
{
for ($x = strlen($y)-1; $x>=0; $x--) {
$y .= $y[$x];
$y[$x] = NULL;
}
echo $y;
}
str_rev("I am a student");
?>
Output:
tneduts a ma I
In the above code, we have passed the value of the string as the parameter.We have performed the string reversal using for loop.
you could use substr with negative start.
Theory & Explanation
you can start with for loop with counter from 1 to length of string, and call substr inside iteration with counter * -1 (which will convert the counter into negative value) and length of 1.
So for the first time counter would be 1 and by multiplying with -1 will turn it to -1
Hence substr('abcdefg', -1, 1); will get you g
and next iteration substr('abcdefg', -2, 1); will get you f
and substr('abcdefg', -3, 1); will get you e
and so on ...
Code
$str = 'abcdefghijklmnopqrstuvwxyz';
for($i=1; $i <= strlen($str); $i++) {
echo substr($str, $i*-1, 1);
}
In Action: https://eval.in/583208
public function checkString($str){
if(!empty($str)){
$i = 0;
$str_reverse = '';
while(isset($str[$i])){
$strArr[] = $str[$i];
$i++;
}
for($j = count($strArr); $j>= 0; $j--){
if(isset($strArr[$j])){
$str_reverse .= $strArr[$j];
}
}
if($str == $str_reverse){
echo 'It is a correct string';
}else{
echo 'Invalid string';
}
}
else{
echo 'string not found.';
}
}
//Reverse String word by word
$str = "Reverse string word by word";
$i = 0;
while ($d = $str[$i]) {
if($d == " ") {
$out = " ".$temp.$out;
$temp = "";
}
else
$temp .= $d;
$i++;
}
echo $temp.$out;
The following solution is very simple, but it does the job:
$string = 'Andreas';
$reversedString = '';
for($i = mb_strlen($string) - 1; $i >= 0; $i--){
$reversedString .= $string[$i];
}
var_dump($reversedString) then results: string(7) "saerdnA"
<?php
$value = 'abcdefg';
$length_value = strlen($value);
for($i = $length_value-1; $i >=0 ;$i--){
echo $value[$i];
}
?>
you can try this..
$string = "NASEEM";
$total_word = strlen($string);
for($i=0; $i<=$total_word; $i++)
{
echo substr($string,$total_word-$i,1);
}
i have used some built in function but without str_rev function .
<?php
$text = "red";
$arr = str_split($text);
$rev_text = array_reverse($arr);
echo join(" ",$rev_text);
?>
Try This
<?php
$str="abcde";
for($i=strlen($str)-1;$i>=0;$i--){
echo $str[$i];
}
?>
output
edcba
This is my solution to solve this.
$in = 'This is a test text';
$out = '';
// find string length
$len = strlen($in);
// loop through it and print it reverse
for ( $i = $len - 1; $i >=0;$i-- )
{
$out = $out.$in[$i];
}
echo $out;
Reverse string using recursion function.
$reverseString = '';
function Reverse($str, $len)
{
if ($len == 0) {
return $GLOBALS['reverseString'];
} else {
$len--;
$GLOBALS['reverseString'] .= $str[$len];
return Reverse($str, $len);
}
}
$str = 'Demo text';
$len = strlen($str);
echo Reverse($str, $len)
Try this
$warn = 'this is a test';
$i=0;
while(#$warn[$i]){
$i++;}
while($i>0)
{
echo $warn[$i-1]; $i--;
}
I have written the following code to count the number of string occurrences in a given file.
PHP
<?php
$p = fopen("g.txt", "r");
$q = fread($p, filesize("g.txt"));
$t = explode(" ", $q);
$m = explode(" ", $q);
$i = 0;
$j = 0;
$r = 0;
$count = 0;
$c = count($t);
$d = array();
echo "count of".
"<br/>";
for ($i = 0; $i < $c; $i++) {
for ($j = $i; $j < $c; $j++) {
if ($t[$i] == $t[$j]) {
$count = $count + 1;
}
}
for ($r = $i + 1; $r < $c; $r++) {
if ($t[$i] == $t[$r])
unset($t[$r]);
}
echo $t[$i].
"=".$count.
"<br/>";
$count = 0;
}
?>
I am getting a notice of undefined offset on line numbers 17 and 24, though my output is coming out to be correct. Can you please help me in rectifying the above problem?
The problem is that you are deleting items from the array $t. You saved the count in $c, but the actual count will change by your last inner loop.
Even if you replace $c by count($t) everywhere, it will go wrong, because the last loop should be in reverse order, otherwise you skip items. For instance if you have the list 'a', 'b', 'c'. then when you delete 'b' and increment $r, you will not check 'c' at all.
So, if I fix those things, your code becomes as below. Although I didn't really check it for other issues. Frankly, I don't really get what is should do. ;-)
<?php
$p=fopen("g.txt","r");
$q=fread($p,filesize("g.txt"));
$t=explode(" ",$q);
$m=explode(" ",$q);
$i=0;
$j=0;
$r=0;
$count=0;
$d=array();
echo "count of"."<br/>";
for($i=0; $i<count($t); $i++)
{
for($j=$i; $j<count($t); $j++)
{
if($t[$i]==$t[$j])
{
$count=$count+1;
}
}
for($r=count($t) - 1; $r > $i; $r--)
{
if($t[$i]==$t[$r])
unset($t[$r]);
}
echo $t[$i]."=".$count."<br/>";
$count=0;
}
?>
In conclusion, you should do more tests. If the outcome of this script was okay, then it was by accident.
I have this simple quicksort function (I got it from uncle "G")
function quicksort( &$list, $l , $r ) {
$i = $l;
$j = $r;
$tmp = $list[(int)( ($l+$r)/2 )];
do {
while( $list[$i] < $tmp )
$i++;
while( $tmp < $list[$j] )
$j--;
if( $i <= $j ) {
$w = $list[$i];
$list[$i] = $list[$j];
$list[$j] = $w;
//_swp($list[$i],$list[$j]);
$i++;
$j--;
}
}while( $i <= $j );
if( $l < $j )
quicksort($list, $l, $j);
if( $i < $r )
quicksort($list, $i, $r);
return $list;
}
And I have this little function to swap two variables.
function _swp(&$a,&$b){
$a=$a+$b;
$b=$a-$b;
$a=$a-$b;
}
How come I can't use _swp($a,$b) in quicksort function instead of this lines?
$w = $list[$i];
$list[$i] = $list[$j];
$list[$j] = $w;
If I comment out these 3 lines of code and enter call to _swp function I got bad results...
Please explain.
Best regards
the unexpected behavior is probably the "random" occurence of zeros in the sorted list. This happens because there is a special case while swapping:
if( $i <= $j ) {
// swapping here using references!
_swp($list[$i],$list[$j]);
$i++;
$j--;
}
The problem is found directly in the condition for swapping itself: if $i==$j then there are two references to the same variable. Thus calling _swp($list[$i],$list[$j]); will firstly add both variables $a = $a + $b. Considering $a and $b actually access the same variable content, $a and $b will then have the same value. In the next step $b = $a - $b will then be zero as $a is equal to $b. The third operation will leave the result to 0.
An easy solution for this is inserting another condition:
if( $i <= $j ) {
// ensure $i to be truly smaller than $j
if( $i < $j ) {
_swp($list[$i],$list[$j]);
}
$i++;
$j--;
}
I hope this will help you.
Cheers,
Fabian
<?php
$i == array(1, 2);
$j == array(a, b);
$m == count($j);
$n == count($i);
for ( $i = 0; $i < $m; i++ )
{
for ( $j = 0; j < $n; j++)
{ echo $i."x"$j; }
}
?>
The error is referencing line 6: for ( $i = 0; $i < $m; i++ )
for ( $i = 0; $i < $m; $i++ )
Note the dollar sign I added before the i++
Same goes for your other for statement:
for ( $j = 0; $j < $n; $j++ )
Wierd error indeed, but it i is not a variable (although PHP might flag a E_NOTICE and convert it to 'i'. You want to reference your variable, so you must add a $ before.
Most likely what you want is:
<?php
$iArray = array(1, 2);
$jArray = array('a', 'b');
$n = count($iArray);
$m = count($jArray);
for ( $i = 0; $i < $n; $i++) {
for ( $j = 0; $j < $m; $j++) {
echo $iArray[$i] . "x" . $jArray[$j];
}
}
?>
The things I changed:
== is used for comparison, = is used for assignment
The second array I assumed you wanted the string literals 'a' and 'b', but you could have also wanted $a and $b if you declared those variables somewhere else
you assign $i to an array, but then in your for loop you overwrite it with $i = 0. You most likely want two variables
missing $s, like I mentioned above
$m was being used for the number of variables in $jArray, but you used it to iterate over $iArray
So just a few pointers, brush up on you PHP and try to make sure your code works with every little change. Make 1 modification, then run it. It is very easy to get lost in syntax for PHP since it is such a dynamic scripting language
You have a bunch of equality checks there. I'm assuming you were actually assigning variables rather than checking for equality.
Change all == equality checks to assignments (=)
You also have improper concatenation on line 9 and I added a comment pointing out another possible error.
$i == array(1, 2);
$j == array($a, $b); // <--Put in $ signs if these are variables in the array
$m == count($j);
$n == count($i);
for ( $i = 0; $i < $m; $i++ )
{
for ( $j = 0; $j < $n; $j++)
{ echo $i."x".$j; }
}