A0Paper

• Time : O(n)
• Space : O(1)

class A0Paper {
public:
    string canBuild(vi& A) {
        if(A[0]) return "Possible";
        ll n = A.size();
        for(ll i = n - 1; i >= 1; i--) {
            A[i-1] += A[i] / 2;
        }
        return A[0] ? "Possible" : "Impossible";
    }
};