private function swap($a, $b) {
        $value            = $this->values[$a];
        $this->values[$a] = $this->values[$b];
        $this->values[$b] = $value;
    }
private function swap($a, $b) {
        $value            = $this->values[$a];
        $this->values[$a] = $this->values[$b];
        $this->values[$b] = $value;
    }
private function swap ( $ a , $ b ) { $ value = $ this -> values [ $ a ] ; $ this -> values [ $ a ] = $ this -> values [ $ b ] ; $ this -> values [ $ b ] = $ value ; }
Swap two values.

@param int $a The first value index.
@param int $b The second value index.
@return void
Swap two values .