Min Stack

题目：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：

这一题本身不存在什么意义，但是需要考虑一些小技巧。

完全可以使用STL。

代码：

class MinStack {
public:
    stack<int>_stack;
    stack<int>_min_stack;
    
    void push(int x) {
        _stack.push(x);
        if(x<=getMin()){
            _min_stack.push(x);
        }
    }

    void pop() {
        if(!_stack.empty()){
            if(_stack.top()==_min_stack.top()){
                _min_stack.pop();
            }
            
            _stack.pop();
        }
    }

    int top() {
        if(!_stack.empty()){
            return _stack.top();
        }
        return 0;
    }

    int getMin() {
        if(!_min_stack.empty()){
            return _min_stack.top();
        }
        return INT_MAX;
    }
};