So while i was doing my homework i stuck on one point.
The excercise is based on making a function which checks if $word is a palindrome, from my tests $L works and is moving forward to right side of the word ($L starts from left, $R from right)
but $R is not working at all, if $R is swapped by a number - it works. If $R is printed, it shows right number - 5.
$word = "madam";
function palindrome($s)
{
$i = intval(strlen($s) / 2);
$L = 0;
$R = strlen($s);
$pal = true;
for($i; $i>0; $i--)
{
if($s[$L] != $s[$R]) $pal=false;
$L++;
$R--;
}
if($pal==true)
print("palindrome");
else
print("not a palindrome");
}
palindrome($word);
I expect to make $R an value, i suspect that PHP sees it as a string, not an integer, but i don't know why. I would be very happy if someone helped me with that.
If you consider string as char table, index starts at 0, but strlen count from 1 so if you have 'madam' then strlen() returns 5 but last chatacter is on $s[4], simply use:
$R = strlen($s)-1;
As a quick, off the top of my head sort of idea... no loops, just some simple string splitting, this works to check if the given string ($s) is a palindrome.
function palindrome($s) {
// split the string in two
$left = substr($s, 0, floor(strlen($s)/2));
$right = substr($s, 0-strlen($left));
// if the left half matches the REVERSE of the right
// you've got a palindrome
return $left === strrev($right);
}
$word = "madam";
echo palindrome($word) ? "Yup" : "Nope";
Basically, it just chops the word in half - reverses the right half and compares it to the left. If they match, it's a palindrome - currently it's case-sensitive though so "Madam" won't be a palindrome but that can be easily tweaked by lower-casing the whole thing first.
Related
I have this array which links numbers to letters at the moment like this:
1-26 = A-Z
But there is more, 27=AA and 28=AB etc...
so basically when I do this:
var_dump($array[2]); //shows B
var_dump($array[29]); //shows AC
Now this array I made myself but it's becoming way too long. Is there a way to actually get this going on till lets say 32? I know there is chr but I dont think I can use this.
Is there an easier way to actually get this without using this way too long of an array?
It's slower calculating it this way, but you can take advantage of the fact that PHP lets you increment letters in the same way as numbers, Perl style:
function excelColumnRange($number) {
$character = 'A';
while ($number > 1) {
++$character;
--$number;
}
return $character;
}
var_dump(excelColumnRange(2));
var_dump(excelColumnRange(29));
here is the code which you are looking for :
<?php
$start = "A";
$max = 50;
$result = array();
for($i=1; $i<=$max; $i++) {
$result[$i] = $start++;
}
print_r($result);
?>
Ref: http://www.xpertdeveloper.com/2011/01/php-strings-unusual-behaviour/
This should work for you:
Even without any loops. First I calculate how many times the alphabet (26) goes into the number. With this I define how many times it has to str_repleat() A. Then I simply subtract this number and calculate the number in the alphabet with the number which is left.
<?php
function numberToLetter($number) {
$fullSets = (($num = floor(($number-1) / 26)) < 0 ? 0 : $num);
return str_repeat("A", $fullSets) . (($v = ($number-$fullSets*26)) > 0 ? chr($v+64) : "");
}
echo numberToLetter(53);
?>
output:
AAA
Since I am still new to PHP, I am looking for a way to find out how to get a specific character from a string.
Example:
$word = "master";
$length = strlen($word);
$random = rand(1,$length);
So let's say the $random value is 3, then I would like to find out what character the third one is, so in this case the character "s". If $random was 2 I would like to know that it's a "a".
I am sure this is really easy, but I tried some substr ideas for nearly an hour now and it always fails.
Your help would be greatly appreciated.
You can use substr() to grab a portion of a string starting from a point and going length. so example would be:
substr('abcde', 1, 1); //returns b
In your case:
$word = "master";
$length = strlen($word) - 1;
$random = rand(0,$length);
echo substr($word, $random, 1);//echos single char at random pos
See it in action here
You can use your string the same like 0-based index array:
$some_string = "apple";
echo $some_string[2];
It'll print 'p'.
or, in your case:
$word = "master";
$length = strlen($word);
$random = rand(0,$length-1);
echo $word[$random];
Try this simply:
$word = "master";
$length = strlen($word);
$random = rand(0,$length-1);
if($word[$random] == 's'){
echo $word[$random];
}
Here I used 0 because $word[0] is m so that we need to subtract one from strlen($word) for getting last character r
Use substr
$GetThis = substr($myStr, 5, 5);
Just use the same values for the same or different if you want multiple characters
$word = "master";
$length = strlen($word);
$random = rand(0,$length-1);
$GetThis = substr($word, $random, $random);
As noted in my comment (I overlooked as well) be sure to start your rand at 0 to include the beginning of your string since the m is at place 0. If we all overlooked that it wouldn't be random (as random?) now would it :)
You can simply use $myStr{$random} to obtain the nth character of the string.
Pattern search within a string.
for eg.
$string = "111111110000";
FindOut($string);
Function should return 0
function FindOut($str){
$items = str_split($str, 3);
print_r($items);
}
If I understand you correctly, your problem comes down to finding out whether a substring of 3 characters occurs in a string twice without overlapping. This will get you the first occurence's position if it does:
function findPattern($string, $minlen=3) {
$max = strlen($string)-$minlen;
for($i=0;$i<=$max;$i++) {
$pattern = substr($string,$i,$minlen);
if(substr_count($string,$pattern)>1)
return $i;
}
return false;
}
Or am I missing something here?
What you have here can conceptually be solved with a sliding window. For your example, you have a sliding window of size 3.
For each character in the string, you take the substring of the current character and the next two characters as the current pattern. You then slide the window up one position, and check if the remainder of the string has what the current pattern contains. If it does, you return the current index. If not, you repeat.
Example:
1010101101
|-|
So, pattern = 101. Now, we advance the sliding window by one character:
1010101101
|-|
And see if the rest of the string has 101, checking every combination of 3 characters.
Conceptually, this should be all you need to solve this problem.
Edit: I really don't like when people just ask for code, but since this seemed to be an interesting problem, here is my implementation of the above algorithm, which allows for the window size to vary (instead of being fixed at 3, the function is only briefly tested and omits obvious error checking):
function findPattern( $str, $window_size = 3) {
// Start the index at 0 (beginning of the string)
$i = 0;
// while( (the current pattern in the window) is not empty / false)
while( ($current_pattern = substr( $str, $i, $window_size)) != false) {
$possible_matches = array();
// Get the combination of all possible matches from the remainder of the string
for( $j = 0; $j < $window_size; $j++) {
$possible_matches = array_merge( $possible_matches, str_split( substr( $str, $i + 1 + $j), $window_size));
}
// If the current pattern is in the possible matches, we found a duplicate, return the index of the first occurrence
if( in_array( $current_pattern, $possible_matches)) {
return $i;
}
// Otherwise, increment $i and grab a new window
$i++;
}
// No duplicates were found, return -1
return -1;
}
It should be noted that this certainly isn't the most efficient algorithm or implementation, but it should help clarify the problem and give a straightforward example on how to solve it.
Looks like you more want to use a sub-string function to walk along and check every three characters and not just break it into 3
function fp($s, $len = 3){
$max = strlen($s) - $len; //borrowed from lafor as it was a terrible oversight by me
$parts = array();
for($i=0; $i < $max; $i++){
$three = substr($s, $i, $len);
if(array_key_exists("$three",$parts)){
return $parts["$three"];
//if we've already seen it before then this is the first duplicate, we can return it
}
else{
$parts["$three"] = i; //save the index of the starting position.
}
}
return false; //if we get this far then we didn't find any duplicate strings
}
Based on the str_split documentation, calling str_split on "1010101101" will result in:
Array(
[0] => 101
[1] => 010
[2] => 110
[3] => 1
}
None of these will match each other.
You need to look at each 3-long slice of the string (starting at index 0, then index 1, and so on).
I suggest looking at substr, which you can use like this:
substr($input_string, $index, $length)
And it will get you the section of $input_string starting at $index of length $length.
quick and dirty implementation of such pattern search:
function findPattern($string){
$matches = 0;
$substrStart = 0;
while($matches < 2 && $substrStart+ 3 < strlen($string) && $pattern = substr($string, $substrStart++, 3)){
$matches = substr_count($string,$pattern);
}
if($matches < 2){
return null;
}
return $substrStart-1;
I have a text file, and I need to pick a random string that is over 6 characters and under 10 characters. Normally, I would use a script like this, which would work, but since it needs to be a certain length, that won't work. Does anybody have a solution to this?
A sample input would be something like this:
Apple
Banana
Orange
Strawberry
Blueberry
Pineapple
Somelongfruithere
Those values would be in a .txt file, each with a line break. An example of a string that would be allowed is pineapple, but apple or Somelongfruithere wouldn't be allowed.
You'll need to do something like this:
$lines = array();
$tmpLines = file('random.txt');
for($i = 0; $i < count($tmpLines); ++$i)
{
if(strlen($tmpLines[ $i ]) > 6 && strlen($tmpLines[ $i ]) < 10)
{
$lines[] = $tmpLines[ $i ];
}
}
$randomWord = $lines[ array_rand($lines) ];
A shorter way, in number of lines, goes like this (but is much less safe):
$randomWord = '';
$lines = file('random.txt');
while(strlen($randomWord) <= 6 || strlen($randomWord) >= 10)
$randomWord = $lines[ array_rand($lines) ];
The first option gets all the lines in the file, and copies only the ones between 6 and 10 chars in length to another array. When choosing a random element from this array, you are "guaranteed" a reasonable access time for any random string.
The second option simply continues to pick a random string until one of the proper length is chosen, but could potentially take a while depending on the random number generator's mood. Unlikely, but I wouldn't want to risk it. Always take reliability as the best approach, in my book.
I would say explode the text file into a variable, run your random generator to get a placement value (position of the random string) then in a loop (a do/while loop), pull the string from the exploded variable, and check it's length to ensure it's what you want
if (strlen($rand_word) > 6 && strlen($rand_word) < 10) {
//execute function and end loop
} else {
// keep checking using a new random placement number
}
The answer depends on the requirement.
If you need to select from a group of strings and only accept one that fits your criteria, then you'll need to use strlen and try again if it is not the correct length.
Otherwise, you're still going to need strlen, to make sure it is at least 6 Chars, but then you can use substr to cut it to 10. If whitespace does not count, use ltrim & rtrim before strlen and substr.
First find all the words that are in the right character range, then pull a random one from the resulting array:
$fileLines = file('somefile.txt');
$myWords = array();
foreach ($fileLines as $line)
{
$thisLine = split(" ",$line);
foreach ($thisLine as $word)
{
$length = strlen($word);
if ($length > 6 && $length < 10)
{
$myWords[] = $word;
}
}
}
$randomWord = $myWords[array_rand($myWords)];
Shortened way!
for ($i=7; $i<=9; $i++)
if (strlen($str) == $i )
echo "bingo! " . strlen($str);
Unfortunately I inherited some code (c/c++) that does some string manipulation and now I need to copy/port that over to php so this functionality can be accessed over the internets.
Specifically the functionality takes some arbitrary strings and "adds" them together. (the c code iterates down the character array and then does some checking to make sure they are in the alphanumeric range)
I can't find specific code examples on how to do this (I am not a PHP developer) - can anyone point me to some resources that will explain this? (basically how to do string/character array manipulation)
EDIT
In response to some comments and answers:
I want the result in ascii, but essentially I will be adding base 36 numbers.
The C code right now converts to base 36 (from ascii)
then "adds" each element together (does not carry - although the original author intended that - and it for some strange reason does the "add" from most significant to least)
Then converts back to ascii.
Strings can be of different lengths
Based on the current answers i think I have enough of what I need. It is always frustrating sometimes learning a new language - you know exactly what you want and you can do it in other languages, just not the one that is for the task at hand...
Thanks for the responses so far.
Can't you just base_convert() them?
$sum = base_convert($str1, 36, 10) + base_convert($str2, 36, 10);
$sum36 = base_convert($sum, 10, 36);
Or do you need arbitrary precision? Here's a stab at arbitrary precision addition, in base 36:
function b36_add($str1, $str2)
{
$to10 = array();
for ($i = 0; $i < 36; ++$i)
{
$to10[base_convert($i, 10, 36)] = $i;
}
$len = max(strlen($str1), strlen($str2));
$str1 = str_repeat('0', $len - strlen($str1)) . $str1;
$str2 = str_repeat('0', $len - strlen($str2)) . $str2;
$pos = $len - 1;
$carry = 0;
$sum = '';
do
{
$tmp = base_convert($carry + $to10[$str1[$pos]] + $to10[$str2[$pos]], 10, 36);
$sum .= substr($tmp, -1);
$carry = (int) substr($tmp, 0, -1);
}
while (--$pos >= 0);
$sum = strrev($sum);
if ($carry)
{
$sum = base_convert($carry, 10, 36) . $sum;
}
return $sum;
}
If you have a string like this in php you can just call the index of an individual character like so:
<?
$x = "Hello";
print $x[0] . "\n";
So in other words, $string_var[n] gives you the nth char, 0-indexed.
First off, I'm assuming you want to add ascii values.
ord() might help you. Based on the other answer, something like:
<?php
function addStrings($x, $y){
// Assumes that both strings are the same length
for($i=0; $i<strlen($x); $i++){
$result[i] = ord($x[i]) + ord($y[i]);
}
return $result;
}
?>
If you use this, you'll probably want to do something if $x and $y are different lengths, but I think it gets the idea across.