⭐Min Stack

Using Pair

vector<pair<int, int>> stk;

MinStack::MinStack() {
    while(stk.size() > 0)
        stk.pop_back();
}

void MinStack::push(int x) {
    if(stk.size() == 0)
        stk.push_back(make_pair(x, x));
    else
        stk.push_back(make_pair(x, min(stk.back().second, x)));
}

void MinStack::pop() {
    if(stk.size() > 0)
        stk.pop_back();
}

int MinStack::top() {
    return ((stk.size() > 0) ? stk.back().first : -1);
}

int MinStack::getMin() {
    return ((stk.size() > 0) ? stk.back().second : -1);
}

Time Complexity: $O(1)$​

Space Complexity: $O(2n)$​ 👈 can be optimized to use $O(n)$​