Task: Determine if a string is squeezable
Java: 

public class StringSqueezable {

    public static void main(String[] args) {
        String[] testStrings = new String[] {
                "", 
                "\"If I were two-faced, would I be wearing this one?\" --- Abraham Lincoln ", 
                "..1111111111111111111111111111111111111111111111111111111111111117777888", 
                "I never give 'em hell, I just tell the truth, and they think it's hell. ", 
                "                                                    --- Harry S Truman  ",
                "122333444455555666666777777788888888999999999",
                "The better the 4-wheel drive, the further you'll be from help when ya get stuck!",
                "headmistressship"};

        String[] testChar = new String[] {
                " ", 
                "-", 
                "7", 
                ".", 
                " -r",
                "5",
                "e",
                "s"};
        for ( int testNum = 0 ; testNum < testStrings.length ; testNum++ ) {
            String s = testStrings[testNum];
            for ( char c : testChar[testNum].toCharArray() ) {
                String result = squeeze(s, c);
                System.out.printf("use: '%c'%nold:  %2d <<<%s>>>%nnew:  %2d <<<%s>>>%n%n", c, s.length(), s, result.length(), result);
            }
        }
    }
    
    private static String squeeze(String in, char include) {
        StringBuilder sb = new StringBuilder();
        for ( int i = 0 ; i < in.length() ; i++ ) {
            if ( i == 0 || in.charAt(i-1) != in.charAt(i) || (in.charAt(i-1) == in.charAt(i) && in.charAt(i) != include)) {
                sb.append(in.charAt(i));
            }
        }
        return sb.toString();
    }

}

PHP: <?php

function squeezeString($string, $squeezeChar) {
    $previousChar = null;
    $squeeze = '';
    $charArray = preg_split('//u', $string, -1, PREG_SPLIT_NO_EMPTY);
    for ($i = 0 ; $i < count($charArray) ; $i++) {
        $currentChar = $charArray[$i];
        if ($previousChar !== $currentChar || $currentChar !== $squeezeChar) {
            $squeeze .= $charArray[$i];
        }
        $previousChar = $currentChar;
    }
    return $squeeze;
}

function isSqueezable($string, $squeezeChar) {
    return ($string !== squeezeString($string, $squeezeChar));
}

$strings = array(
    ['-', '"If I were two-faced, would I be wearing this one?" --- Abraham Lincoln '],
    ['1', '..1111111111111111111111111111111111111111111111111111111111111117777888'],
    ['l', "I never give 'em hell, I just tell the truth, and they think it's hell. "],
    [' ', '                                                    --- Harry S Truman  '],
    ['9', '0112223333444445555556666666777777778888888889999999999'],
    ['e', "The better the 4-wheel drive, the further you'll be from help when ya get stuck!"],
    ['k', "The better the 4-wheel drive, the further you'll be from help when ya get stuck!"],
);
foreach ($strings as $params) {
    list($char, $original) = $params;
    echo 'Original   : <<<', $original, '>>> (len=', mb_strlen($original), ')', PHP_EOL;
    if (isSqueezable($original, $char)) {
        $squeeze = squeezeString($original, $char);
        echo 'Squeeze(', $char, ') : <<<', $squeeze, '>>> (len=', mb_strlen($squeeze), ')', PHP_EOL, PHP_EOL;
    } else {
        echo 'Squeeze(', $char, ') : string is not squeezable (char=', $char, ')...', PHP_EOL, PHP_EOL;
    }
}