bool isHappy(int n) {
int slow = n, fast = n;
do {
slow = squareDigits(slow);
fast = squareDigits(squareDigits(fast));
} while (slow != fast);
return fast == 1;
}
int oneOr89(int n, int cache[]) {
return cache[squareDigits(n) - 1];
}
int oneOr89(int n) {
while (n != 1 && n != 89) {
n = squareDigits(n);
}
return n;
}
