AND Product

• Time : O(log(min(a,b)))
• Space : O(1)

long andProduct(long a, long b) {
    if(!a or !b) return 0;
    long lga = log2(a), lgb = log2(b);
    if(lga == lgb) return (1ll<<lga) + andProduct(a ^ (1ll<<lga), b ^ (1ll<<lga));
    return 0;
}