Min Stack（C++最小棧）

解題思路：

（1）設置兩個數組，一個保存原始順序，一個保存最小值

（2）注意出棧時，重新設置當前最小值

class MinStack {
public:
    /** initialize your data structure here. */
    vector<int> v,min_v;
	int m = INT_MAX;
    
    MinStack() {}
    
    void push(int x) {
        v.push_back(x);
		if (x<=m) min_v.push_back(x),m=x;
		else min_v.push_back(m);
    }
    
    void pop() {
        if (v.size()!=0) v.pop_back(),min_v.pop_back();
        if (v.size()==0) m = INT_MAX; // 重置最小值
        else m = getMin();
    }
    
    int top() {
        if (v.size()!=0) return *v.rbegin();
        return -1;
    }
    
    int getMin() {
        if (v.size()!=0) return *min_v.rbegin();
        return -1;
    }
};

/**
 * 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();
 */