/*
Six different functions that accept 5 or 7
and return the other number, without using if/switch.
*/
/* 1. Arithmetic sum trick: 5 + 7 = 12 */
function flip_sum($x) {
return 12 - $x;
}
/* 2. Product trick: 5 * 7 = 35 */
function flip_product($x) {
return 35 / $x;
}
/* 3. XOR trick: 5 ^ 7 = 2
x ^ 2 flips 5 ↔ 7 */
function flip_xor($x) {
return $x ^ 2;
}
/* 4. Modulo-based trick using divisibility:
$x % 7 == 0 → x is 7
$x % 5 == 0 → x is 5
Boolean → int via (int) cast */
function flip_mod($x) {
return 5 * (int)($x % 7 == 0)
+ 7 * (int)($x % 5 == 0);
}
/* 5. Absolute-value trick: |x - 12| flips 5 ↔ 7 */
function flip_abs($x) {
return abs($x - 12);
}
/* 6. Array lookup using arithmetic index:
For x = 5 → (5 - 5) / 2 = 0 → table[0] = 7
For x = 7 → (7 - 5) / 2 = 1 → table[1] = 5 */
function flip_array($x) {
$table = [7, 5];
$index = ($x - 5) / 2;
return $table[$index];
}
echo "flip_sum(5) = " . flip_sum(5) . PHP_EOL;
echo "flip_sum(7) = " . flip_sum(7) . PHP_EOL . PHP_EOL;
echo "flip_product(5) = " . flip_product(5) . PHP_EOL;
echo "flip_product(7) = " . flip_product(7) . PHP_EOL . PHP_EOL;
echo "flip_xor(5) = " . flip_xor(5) . PHP_EOL;
echo "flip_xor(7) = " . flip_xor(7) . PHP_EOL . PHP_EOL;
echo "flip_mod(5) = " . flip_mod(5) . PHP_EOL;
echo "flip_mod(7) = " . flip_mod(7) . PHP_EOL . PHP_EOL;
echo "flip_abs(5) = " . flip_abs(5) . PHP_EOL;
echo "flip_abs(7) = " . flip_abs(7) . PHP_EOL . PHP_EOL;
echo "flip_array(5) = " . flip_array(5) . PHP_EOL;
echo "flip_array(7) = " . flip_array(7) . PHP_EOL;
/*
OUTPUT:
flip_sum(5) = 7
flip_sum(7) = 5
flip_product(5) = 7
flip_product(7) = 5
flip_xor(5) = 7
flip_xor(7) = 5
flip_mod(5) = 7
flip_mod(7) = 5
flip_abs(5) = 7
flip_abs(7) = 5
flip_array(5) = 7
flip_array(7) = 5
*/
