Minimum Loss

• Time : O(nlogn)
• Space : O(n)

int minimumLoss(vector<long> A) {
    long res = INT_MAX, n = A.size();
    set<long> s;
    for(int i = n - 1; i >= 0; i--) {
        auto it = s.lower_bound(A[i]);
        if(it != begin(s)) res = min(res, A[i] - *prev(it));
        s.insert(A[i]);
    }

    return res;
}