155. Min Stack

简单题，建立一个helper，存储最小值。

class MinStack {private:    stack<int> nums;    stack<int> helper;public:    /** initialize your data structure here. */    MinStack() {    }    void push(int x) {        nums.push(x);        if(helper.empty())            helper.push(x);        else        {            //helper.push(x);            int temp=helper.top();            if(x<temp)                helper.push(x);            else                helper.push(temp);        }        //helper.push(x);    }    void pop() {        nums.pop();        helper.pop();    }    int top() {        return nums.top();    }    int getMin() {        return helper.top();    }};/** * Your MinStack object will be instantiated and called as such: * MinStack obj = new MinStack(); * obj.push(x); * obj.pop(); * int param_3 = obj.top(); * int param_4 = obj.getMin(); */