Question

php please

// 2) mirrorEnds

// Complete method mirrorEnds that given a string, looks for a mirror

// image (backwards) string at both the beginning and end of the given string.

// In other words, zero or more characters at the very beginning of the given

// string, and at the very end of the string in reverse order (possibly overlapping).

// For example, "abXYZba" has the mirror end "ab".

//

// assert("" == mirrorEnds(""));

// assert("" == mirrorEnds("abcde"));

// assert("a" == mirrorEnds("abca"));

// assert("aba" == mirrorEnds("aba"));

//

function mirrorEnds($str) {

}

echo PHP_EOL . "mirrorEnds(abcdefcba) abc: " . mirrorEnds ( 'abcdefcba' ) . "\n";

assert ( 'abc' == mirrorEnds ( 'abcdefcba' ) );

echo " mirrorEnds(zzRSTzz) zz: " . mirrorEnds ( 'zzRSTzz' ) . "\n";

Answer 1

The code is given below followed by the output snapshot for some test cases. The basic logic used is as follows: A copy of the reversed string is made, and then compared with the original character by character - as soon as a mismatch is found, the loop is broken.

function mirrorEnds($str) {
$rev = strrev($str);
$mir_end = "";

for($i = 0; $i < strlen($str); ++$i)
{
    if($rev[$i] != $str[$i])
      break;
    $mir_end = $mir_end . $str[$i];
}
return $mir_end;
}

echo PHP_EOL . "mirrorEnds(abcdefcba) abc: " . mirrorEnds ( 'abcdefcba' ) . "\n";
echo " mirrorEnds(zzRSTzz) zz: " . mirrorEnds ( 'zzRSTzz' ) . "\n";
echo " mirrorEnds() : " . mirrorEnds ('') . "\n";
echo " mirrorEnds(abcde) : " . mirrorEnds('abcde') . "\n";
echo " mirrorEnds('abca') a: " . mirrorEnds('abca') . "\n";
echo " mirrorEnds('aba') aba: " . mirrorEnds('aba') . "\n";