[LeetCode]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.

思路：利用两个栈，一个栈存储数据，一个栈采用DP的思想，动态存储当前数据的最小值，这样相当于实现了O(1)的最小值。

class MinStack {
public:
    void push(int x) {
        data.push(x);
        if(min.size()==0) //空的时候压入最小栈
            min.push(x);
        else
        {
            if(x<min.top()) 
            {
                min.push(x);
            }
            else if(x>=min.top())
                min.push(min.top());
        }
    }

    void pop() {
        data.pop();
        min.pop();
    }

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

    int getMin() {
        return min.top();
    }
private:
    stack<int> data;
    stack<int> min; 
};