155. Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

class MinStack {
public:
    stack<int> t1;
    stack<int> t2;//保存最小值
    
    void push(int x) {
        t1.push(x);
        if(t2.empty() || x <=t2.top())
            t2.push(x);
    }

    void pop() {
        if(t1.top() == t2.top())
        {
            t1.pop();
            t2.pop();
        }
        else {
            t1.pop();
        }
    }

    int top() {
        return t1.top();
    }

    int getMin() {
        return t2.top();
    }
};